Update reported elftoolchain version

The last elftoolchain update is upstream rev 3136. Update our reported
version and add M (Modified) suffix as our elftoolchain contains
additional fixes not yet committed upstream.

Sponsored by:	The FreeBSD Foundation

lib/libelftc/elftc_version.c

@@ -6,5 +6,5 @@
 const char *
 elftc_version(void)
 {
-	return "libelftc r3130";
+	return "elftoolchain r3136M";
 }