Sync toplevel with upstream GCC.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

config/bitfields.m4

@@ -0,0 +1,25 @@
+dnl Copyright (C) 2015 Free Software Foundation, Inc.
+dnl This file is free software, distributed under the terms of the GNU
+dnl General Public License.  As a special exception to the GNU General
+dnl Public License, this file may be distributed as part of a program
+dnl that contains a configuration script generated by Autoconf, under
+dnl the same distribution terms as the rest of that program.
+
+# Define HAVE_BITFIELD_TYPE_MATTERS if the type of bitfields effects their
+# alignment.
+
+AC_DEFUN([gt_BITFIELD_TYPE_MATTERS],
+[
+  AC_CACHE_CHECK([if the type of bitfields matters], gt_cv_bitfield_type_matters,
+  [
+    AC_TRY_COMPILE(
+      [struct foo1 { char x; char y:1; char z; };
+struct foo2 { char x; long long int y:1; char z; };
+int foo1test[ sizeof (struct foo1) < sizeof (struct foo2) ? 1 : -1 ]; ],
+      [], gt_cv_bitfield_type_matters=yes, gt_cv_bitfield_type_matters=no)
+  ])
+  if test $gt_cv_bitfield_type_matters = yes; then
+    AC_DEFINE(HAVE_BITFIELD_TYPE_MATTERS, 1,
+      [Define if the type of bitfields effects alignment.])
+  fi
+])