Added a define check for __x86_64__.

configure

@@ -18414,6 +18414,37 @@ if test $ac_cv_cpp_def___i386__ = yes; then
   LINTFLAGS="$LINTFLAGS -D__i386__"
 fi
  ;;
+  *x86_64*)         echo "$as_me:$LINENO: checking whether we need to define __x86_64__" >&5
+echo $ECHO_N "checking whether we need to define __x86_64__... $ECHO_C" >&6
+if test "${ac_cv_cpp_def___x86_64__+set}" = set; then
+  echo $ECHO_N "(cached) $ECHO_C" >&6
+else
+  cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+#ifndef __x86_64__
+yes
+#endif
+_ACEOF
+if (eval "$ac_cpp conftest.$ac_ext") 2>&5 |
+  $EGREP "yes" >/dev/null 2>&1; then
+  ac_cv_cpp_def___x86_64__=yes
+else
+  ac_cv_cpp_def___x86_64__=no
+fi
+rm -f conftest*
+
+fi
+echo "$as_me:$LINENO: result: $ac_cv_cpp_def___x86_64__" >&5
+echo "${ECHO_T}$ac_cv_cpp_def___x86_64__" >&6
+if test $ac_cv_cpp_def___x86_64__ = yes; then
+  CFLAGS="$CFLAGS -D__x86_64__"
+  LINTFLAGS="$LINTFLAGS -D__x86_64__"
+fi
+ ;;
   *alpha*)          echo "$as_me:$LINENO: checking whether we need to define __ALPHA__" >&5
 echo $ECHO_N "checking whether we need to define __ALPHA__... $ECHO_C" >&6
 if test "${ac_cv_cpp_def___ALPHA__+set}" = set; then

configure.ac

@@ -1435,6 +1435,7 @@ dnl *** check for the need to define platform-specific symbols
 
 case $host_cpu in
   *i[[3456789]]86*) WINE_CHECK_DEFINE([__i386__]) ;;
+  *x86_64*)         WINE_CHECK_DEFINE([__x86_64__]) ;;
   *alpha*)          WINE_CHECK_DEFINE([__ALPHA__]) ;;
   *sparc*)          WINE_CHECK_DEFINE([__sparc__]) ;;
   *powerpc*)        WINE_CHECK_DEFINE([__powerpc__]) ;;