Import new gnulib.

m4/stdalign.m4

@@ -0,0 +1,52 @@
+# Check for stdalign.h that conforms to C11.
+
+dnl Copyright 2011-2013 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+# Prepare for substituting <stdalign.h> if it is not supported.
+
+AC_DEFUN([gl_STDALIGN_H],
+[
+  AC_CACHE_CHECK([for working stdalign.h],
+    [gl_cv_header_working_stdalign_h],
+    [AC_COMPILE_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[#include <stdalign.h>
+            #include <stddef.h>
+
+            /* Test that alignof yields a result consistent with offsetof.
+               This catches GCC bug 52023
+               <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.  */
+            #ifdef __cplusplus
+               template <class t> struct alignof_helper { char a; t b; };
+            # define ao(type) offsetof (alignof_helper<type>, b)
+            #else
+            # define ao(type) offsetof (struct { char a; type b; }, b)
+            #endif
+            char test_double[ao (double) % _Alignof (double) == 0 ? 1 : -1];
+            char test_long[ao (long int) % _Alignof (long int) == 0 ? 1 : -1];
+            char test_alignof[alignof (double) == _Alignof (double) ? 1 : -1];
+
+            /* Test _Alignas only on platforms where gnulib can help.  */
+            #if \
+                (__GNUC__ || __IBMC__ || __IBMCPP__ \
+                 || 0x5110 <= __SUNPRO_C || 1300 <= _MSC_VER)
+              struct alignas_test { char c; char alignas (8) alignas_8; };
+              char test_alignas[offsetof (struct alignas_test, alignas_8) == 8
+                                ? 1 : -1];
+            #endif
+          ]])],
+       [gl_cv_header_working_stdalign_h=yes],
+       [gl_cv_header_working_stdalign_h=no])])
+
+  if test $gl_cv_header_working_stdalign_h = yes; then
+    STDALIGN_H=''
+  else
+    STDALIGN_H='stdalign.h'
+  fi
+
+  AC_SUBST([STDALIGN_H])
+  AM_CONDITIONAL([GL_GENERATE_STDALIGN_H], [test -n "$STDALIGN_H"])
+])