Fix bootstrap failure for bare metal due to autoconf link tests

The AC_CHECK_FUNCS tests cause the build to fail for bare metal cross
compilers, where link tests are not allowed. Replace them with
GCC_TRY_COMPILE_OR_LINK tests instead. Skip all the Filesystem
dependency checks if not building the filesystem library.

	* acinclude.m4 (GLIBCXX_CHECK_FILESYSTEM_DEPS): Only check when
	enable_libstdcxx_filesystem_ts = yes. Check for link, readlink and
	symlink.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Remove AC_CHECK_FUNCS for link, readlink and symlink.

From-SVN: r261704

libstdc++-v3/ChangeLog

@@ -1,5 +1,12 @@
 2018-06-18  Jonathan Wakely  <jwakely@redhat.com>
 
+	* acinclude.m4 (GLIBCXX_CHECK_FILESYSTEM_DEPS): Only check when
+	enable_libstdcxx_filesystem_ts = yes. Check for link, readlink and
+	symlink.
+	* config.h.in: Regenerate.
+	* configure: Regenerate.
+	* configure.ac: Remove AC_CHECK_FUNCS for link, readlink and symlink.
+
 	LWG 3035. std::allocator's constructors should be constexpr
 	* include/bits/allocator.h (allocator): Add constexpr to constructors
 	for C++2a. Replace dynamic exception specifications with NOTHROW

libstdc++-v3/acinclude.m4

@@ -4309,11 +4309,22 @@ AC_DEFUN([GLIBCXX_ENABLE_FILESYSTEM_TS], [
 ])
 
 dnl
-dnl Check whether the library calls required by the Filesystem TS are present
+dnl Check whether the library calls required by the Filesystem TS are present.
-dnl and define _GLIBCXX_USE_REALPATH and _GLIBCXX_USE_UTIMENSAT.
+dnl Defines:
+dnl  HAVE_STRUCT_DIRENT_D_TYPE
+dnl  _GLIBCXX_USE_REALPATH
+dnl  _GLIBCXX_USE_UTIMENSAT
+dnl  _GLIBCXX_USE_ST_MTIM
+dnl  _GLIBCXX_USE_FCHMOD
+dnl  _GLIBCXX_USE_FCHMODAT
+dnl  _GLIBCXX_USE_SENDFILE
+dnl  HAVE_LINK
+dnl  HAVE_READLINK
+dnl  HAVE_SYMLINK
 dnl
 AC_DEFUN([GLIBCXX_CHECK_FILESYSTEM_DEPS], [dnl
 dnl
+  if test $enable_libstdcxx_filesystem_ts = yes; then
     AC_LANG_SAVE
     AC_LANG_CPLUSPLUS
     ac_save_CXXFLAGS="$CXXFLAGS"
@@ -4443,9 +4454,49 @@ dnl
       AC_DEFINE(_GLIBCXX_USE_SENDFILE, 1, [Define if sendfile is available in <sys/sendfile.h>.])
     fi
     AC_MSG_RESULT($glibcxx_cv_sendfile)
+dnl
+    AC_MSG_CHECKING([for link])
+    AC_CACHE_VAL(glibcxx_cv_link, [dnl
+      GCC_TRY_COMPILE_OR_LINK(
+        [#include <unistd.h>],
+        [link("", "");],
+        [glibcxx_cv_link=yes],
+        [glibcxx_cv_link=no])
+    ])
+    if test $glibcxx_cv_link = yes; then
+      AC_DEFINE(HAVE_LINK, 1, [Define if link is available in <unistd.h>.])
+    fi
+    AC_MSG_RESULT($glibcxx_cv_link)
+dnl
+    AC_MSG_CHECKING([for readlink])
+    AC_CACHE_VAL(glibcxx_cv_readlink, [dnl
+      GCC_TRY_COMPILE_OR_LINK(
+        [#include <unistd.h>],
+        [char buf[32]; readlink("", buf, sizeof(buf));],
+        [glibcxx_cv_readlink=yes],
+        [glibcxx_cv_readlink=no])
+    ])
+    if test $glibcxx_cv_readlink = yes; then
+      AC_DEFINE(HAVE_READLINK, 1, [Define if readlink is available in <unistd.h>.])
+    fi
+    AC_MSG_RESULT($glibcxx_cv_readlink)
+dnl
+    AC_MSG_CHECKING([for symlink])
+    AC_CACHE_VAL(glibcxx_cv_symlink, [dnl
+      GCC_TRY_COMPILE_OR_LINK(
+        [#include <unistd.h>],
+        [symlink("", "");],
+        [glibcxx_cv_symlink=yes],
+        [glibcxx_cv_symlink=no])
+    ])
+    if test $glibcxx_cv_symlink = yes; then
+      AC_DEFINE(HAVE_SYMLINK, 1, [Define if symlink is available in <unistd.h>.])
+    fi
+    AC_MSG_RESULT($glibcxx_cv_symlink)
 dnl
     CXXFLAGS="$ac_save_CXXFLAGS"
     AC_LANG_RESTORE
+  fi
 ])
 
 dnl

libstdc++-v3/config.h.in

@@ -264,7 +264,7 @@
 /* Only used in build directory testsuite_hooks.h. */
 #undef HAVE_LIMIT_VMEM
 
-/* Define to 1 if you have the `link' function. */
+/* Define if link is available in <unistd.h>. */
 #undef HAVE_LINK
 
 /* Define if futex syscall is available. */
@@ -342,7 +342,7 @@
 /* Define to 1 if you have the `quick_exit' function. */
 #undef HAVE_QUICK_EXIT
 
-/* Define to 1 if you have the `readlink' function. */
+/* Define if readlink is available in <unistd.h>. */
 #undef HAVE_READLINK
 
 /* Define to 1 if you have the `setenv' function. */
@@ -414,7 +414,7 @@
 /* Define if strxfrm_l is available in <string.h>. */
 #undef HAVE_STRXFRM_L
 
-/* Define to 1 if you have the `symlink' function. */
+/* Define if symlink is available in <unistd.h>. */
 #undef HAVE_SYMLINK
 
 /* Define to 1 if the target runtime linker supports binding the same symbol

libstdc++-v3/configure

@@ -80047,19 +80047,6 @@ _ACEOF
 
 fi
 
-done
-
-for ac_func in link readlink symlink
-do :
-  as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
-ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
-eval as_val=\$$as_ac_var
-   if test "x$as_val" = x""yes; then :
-  cat >>confdefs.h <<_ACEOF
-#define `$as_echo "HAVE_$ac_func" | $as_tr_cpp` 1
-_ACEOF
-
-fi
 done
 
 
@@ -80105,6 +80092,7 @@ $as_echo_n "checking whether to build Filesystem TS support... " >&6; }
 $as_echo "$enable_libstdcxx_filesystem_ts" >&6; }
 
 
+  if test $enable_libstdcxx_filesystem_ts = yes; then
 
     ac_ext=cpp
 ac_cpp='$CXXCPP $CPPFLAGS'
@@ -80567,6 +80555,174 @@ $as_echo "#define _GLIBCXX_USE_SENDFILE 1" >>confdefs.h
     fi
     { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_sendfile" >&5
 $as_echo "$glibcxx_cv_sendfile" >&6; }
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for link" >&5
+$as_echo_n "checking for link... " >&6; }
+    if test "${glibcxx_cv_link+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+        if test x$gcc_no_link = xyes; then
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <unistd.h>
+int
+main ()
+{
+link("", "");
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_link=yes
+else
+  glibcxx_cv_link=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+  if test x$gcc_no_link = xyes; then
+  as_fn_error "Link tests are not allowed after GCC_NO_EXECUTABLES." "$LINENO" 5
+fi
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <unistd.h>
+int
+main ()
+{
+link("", "");
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+  glibcxx_cv_link=yes
+else
+  glibcxx_cv_link=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+
+fi
+
+    if test $glibcxx_cv_link = yes; then
+
+$as_echo "#define HAVE_LINK 1" >>confdefs.h
+
+    fi
+    { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_link" >&5
+$as_echo "$glibcxx_cv_link" >&6; }
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for readlink" >&5
+$as_echo_n "checking for readlink... " >&6; }
+    if test "${glibcxx_cv_readlink+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+        if test x$gcc_no_link = xyes; then
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <unistd.h>
+int
+main ()
+{
+char buf[32]; readlink("", buf, sizeof(buf));
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_readlink=yes
+else
+  glibcxx_cv_readlink=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+  if test x$gcc_no_link = xyes; then
+  as_fn_error "Link tests are not allowed after GCC_NO_EXECUTABLES." "$LINENO" 5
+fi
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <unistd.h>
+int
+main ()
+{
+char buf[32]; readlink("", buf, sizeof(buf));
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+  glibcxx_cv_readlink=yes
+else
+  glibcxx_cv_readlink=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+
+fi
+
+    if test $glibcxx_cv_readlink = yes; then
+
+$as_echo "#define HAVE_READLINK 1" >>confdefs.h
+
+    fi
+    { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_readlink" >&5
+$as_echo "$glibcxx_cv_readlink" >&6; }
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for symlink" >&5
+$as_echo_n "checking for symlink... " >&6; }
+    if test "${glibcxx_cv_symlink+set}" = set; then :
+  $as_echo_n "(cached) " >&6
+else
+        if test x$gcc_no_link = xyes; then
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <unistd.h>
+int
+main ()
+{
+symlink("", "");
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_symlink=yes
+else
+  glibcxx_cv_symlink=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+  if test x$gcc_no_link = xyes; then
+  as_fn_error "Link tests are not allowed after GCC_NO_EXECUTABLES." "$LINENO" 5
+fi
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <unistd.h>
+int
+main ()
+{
+symlink("", "");
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+  glibcxx_cv_symlink=yes
+else
+  glibcxx_cv_symlink=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+
+fi
+
+    if test $glibcxx_cv_symlink = yes; then
+
+$as_echo "#define HAVE_SYMLINK 1" >>confdefs.h
+
+    fi
+    { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_symlink" >&5
+$as_echo "$glibcxx_cv_symlink" >&6; }
     CXXFLAGS="$ac_save_CXXFLAGS"
     ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
@@ -80574,6 +80730,7 @@ ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
 ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
+  fi
 
 
 # For Transactional Memory TS

libstdc++-v3/configure.ac

@@ -420,7 +420,6 @@ GLIBCXX_CHECK_GTHREADS
 
 # For Filesystem TS.
 AC_CHECK_HEADERS([fcntl.h dirent.h sys/statvfs.h utime.h])
-AC_CHECK_FUNCS(link readlink symlink)
 GLIBCXX_ENABLE_FILESYSTEM_TS
 GLIBCXX_CHECK_FILESYSTEM_DEPS