Guard against M4 versions with a buggy strstr.

config/:
	* override.m4: Error out if a buggy M4 was detected, to
	avoid spurious diffs in generated files.

Co-Authored-By: Eric Blake <eblake@redhat.com>

From-SVN: r170697

config/ChangeLog

+2011-03-05  Ralf Wildenhues  <Ralf.Wildenhues@gmx.de>
+	    Eric Blake  <eblake@redhat.com>
+
+	* override.m4: Error out if a buggy M4 was detected, to
+	avoid spurious diffs in generated files.
+
 2011-01-25  Jakub Jelinek  <jakub@redhat.com>
 
 	* cloog.m4 (CLOOG_REQUESTED): Use $2 if --without-cloog.

config/override.m4

@@ -48,6 +48,12 @@ _GCC_AUTOCONF_VERSION_CHECK
 ])
 
 
+dnl Ensure we do not use a buggy M4.
+m4_if(m4_index([..wi.d.], [.d.]), [-1],
+  [m4_fatal(m4_do([m4 with buggy strstr detected.  Please install
+GNU M4 1.4.16 or newer and set the M4 environment variable]))])
+
+
 dnl Fix 2.64 cross compile detection for AVR and RTEMS
 dnl by not trying to compile fopen.
 m4_if(m4_defn([m4_PACKAGE_VERSION]), [2.64],