From 74106ead26b17f3e68b73c6704632cbbbf762a5c Mon Sep 17 00:00:00 2001
From: George Lander <george.lander@arm.com>
Date: Fri, 10 Mar 2017 12:22:45 +0000
Subject: [PATCH] [libstdc++-v3] Fix detection of obsolete isnan

libstdc++-v3 configure checks whether old glibc inline definitions
of isnan would conflict with the libstdc++-v3 definitions and
works around them if so.  But if g++ 6.x build A is used to build
another g++ 6.x B, the configure step for B will pick up the math.h
installed alongside A instead of the glibc version.  configure will
then assume that the workaround isn't necessary, leaving B with a
broken cmath.

isinf already worked around this.  This patch extends the same fix
to isnan.  (Thanks to George for the fix.)

libstdc++-v3/
2017-03-10  George Lander  <george.lander@arm.com>

	* acinclude.m4 (glibcxx_cv_obsolete_isnan): Define
	_GLIBCXX_INCLUDE_NEXT_C_HEADERS before including math.h.
	* configure: Regenerate.

From-SVN: r246025
---
 libstdc++-v3/ChangeLog    | 6 ++++++
 libstdc++-v3/acinclude.m4 | 3 ++-
 libstdc++-v3/configure    | 1 +
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 9da31bc984a..d94f6d4831e 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,9 @@
+2017-03-10  George Lander  <george.lander@arm.com>
+
+	* acinclude.m4 (glibcxx_cv_obsolete_isnan): Define
+	_GLIBCXX_INCLUDE_NEXT_C_HEADERS before including math.h.
+	* configure: Regenerate.
+
 2017-03-09  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/std/functional (_Not_fn): Define macro to simplify
diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index d9859aaf029..5998fe6fdee 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -2297,7 +2297,8 @@ AC_DEFUN([GLIBCXX_CHECK_MATH11_PROTO], [
       AC_MSG_CHECKING([for obsolete isnan function in <math.h>])
         AC_CACHE_VAL(glibcxx_cv_obsolete_isnan, [
           AC_COMPILE_IFELSE([AC_LANG_SOURCE(
-            [#include <math.h>
+            [#define _GLIBCXX_INCLUDE_NEXT_C_HEADERS
+             #include <math.h>
              #undef isnan
              namespace std {
                using ::isnan;
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 9bb986222ca..29456c4421e 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -18390,6 +18390,7 @@ else
 
           cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
+#define _GLIBCXX_INCLUDE_NEXT_C_HEADERS
 #include <math.h>
              #undef isnan
              namespace std {