re PR go/67874 (fd_unix.go does not build when there is fcntl64 and no fcntl syscall)

PR go/67874
    net, runtime: Call C library fcntl function rather than syscall.Syscall.
    
    Not all systems define a fcntl syscall; some only have fcntl64.
    
    Fixes GCC PR go/67874.
    
    Reviewed-on: https://go-review.googlesource.com/15497

From-SVN: r228576

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-3039d79149901d25d89c2412bdd8684f3cbcd09e
+651e71a729e5dcbd9dc14c1b59b6eff05bfe3d26
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/net/fd_unix.go

@@ -442,13 +442,21 @@ func (fd *netFD) accept() (netfd *netFD, err error) {
 	return netfd, nil
 }
 
+// Use a helper function to call fcntl.  This is defined in C in
+// libgo/runtime.
+//extern __go_fcntl_uintptr
+func fcntl(uintptr, uintptr, uintptr) (uintptr, uintptr)
+
 // tryDupCloexec indicates whether F_DUPFD_CLOEXEC should be used.
 // If the kernel doesn't support it, this is set to 0.
 var tryDupCloexec = int32(1)
 
 func dupCloseOnExec(fd int) (newfd int, err error) {
 	if atomic.LoadInt32(&tryDupCloexec) == 1 && syscall.F_DUPFD_CLOEXEC != 0 {
-		r0, _, e1 := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_DUPFD_CLOEXEC, 0)
+		syscall.Entersyscall()
+		r0, errno := fcntl(uintptr(fd), syscall.F_DUPFD_CLOEXEC, 0)
+		syscall.Exitsyscall()
+		e1 := syscall.Errno(errno)
 		if runtime.GOOS == "darwin" && e1 == syscall.EBADF {
 			// On OS X 10.6 and below (but we only support
 			// >= 10.6), F_DUPFD_CLOEXEC is unsupported

libgo/runtime/go-varargs.c

@@ -6,6 +6,8 @@
 
 #include "config.h"
 
+#include <errno.h>
+#include <stdint.h>
 #include <sys/types.h>
 #include <fcntl.h>
 
@@ -32,6 +34,28 @@ __go_fcntl_flock (int fd, int cmd, struct flock *arg)
   return fcntl (fd, cmd, arg);
 }
 
+// This is for the net package.  We use uintptr_t to make sure that
+// the types match, since the Go and C "int" types are not the same.
+struct go_fcntl_ret {
+  uintptr_t r;
+  uintptr_t err;
+};
+
+struct go_fcntl_ret
+__go_fcntl_uintptr (uintptr_t fd, uintptr_t cmd, uintptr_t arg)
+{
+  int r;
+  struct go_fcntl_ret ret;
+
+  r = fcntl ((int) fd, (int) cmd, (int) arg);
+  ret.r = (uintptr_t) r;
+  if (r < 0)
+    ret.err = (uintptr_t) errno;
+  else
+    ret.err = 0;
+  return ret;
+}
+
 #ifdef HAVE_OPEN64
 
 int