Port AC_C_BIGENDIAN to cross gcc -std=c11 -flto

* lib/autoconf/c.m4 (AC_C_BIGENDIAN): Improve the
inherently-unportable grep trick well enough to survive gcc
-std=c11 -flto when cross-compiling (sr#110687).

diff --git a/lib/autoconf/c.m4 b/lib/autoconf/c.m4
index b0c2bf84783e2be92258684f517031e9dcb4f98b..abbb83fe654932cf3bd005a822ad8477bd3b0a02 100644 (file)
--- a/lib/autoconf/c.m4
+++ b/lib/autoconf/c.m4
@@ -1838,8 +1838,8 @@ AC_DEFUN([AC_C_BIGENDIAN],
        [ac_cv_c_bigendian=no],
        [ac_cv_c_bigendian=yes],
        [# Try to guess by grepping values from an object file.
-        AC_COMPILE_IFELSE(
-          [AC_LANG_PROGRAM(
+        AC_LINK_IFELSE(
+          [AC_LANG_SOURCE(
              [[unsigned short int ascii_mm[] =
                  { 0x4249, 0x4765, 0x6E44, 0x6961, 0x6E53, 0x7953, 0 };
                unsigned short int ascii_ii[] =
@@ -1854,13 +1854,20 @@ AC_DEFUN([AC_C_BIGENDIAN],
                int use_ebcdic (int i) {
                  return ebcdic_mm[i] + ebcdic_ii[i];
                }
-               extern int foo;
-             ]],
-             [[return use_ascii (foo) == use_ebcdic (foo);]])],
-          [if grep BIGenDianSyS conftest.$ac_objext >/dev/null; then
+               int
+               main (int argc, char **argv)
+               {
+                 /* Intimidate the compiler so that it does not
+                    optimize the arrays away.  */
+                 char *p = argv[0];
+                 ascii_mm[1] = *p++; ebcdic_mm[1] = *p++;
+                 ascii_ii[1] = *p++; ebcdic_ii[1] = *p++;
+                 return use_ascii (argc) == use_ebcdic (*p);
+               }]])],
+          [if grep BIGenDianSyS conftest$ac_exeext >/dev/null; then
              ac_cv_c_bigendian=yes
            fi
-           if grep LiTTleEnDian conftest.$ac_objext >/dev/null ; then
+           if grep LiTTleEnDian conftest$ac_exeext >/dev/null ; then
              if test "$ac_cv_c_bigendian" = unknown; then
                ac_cv_c_bigendian=no
              else