Treat irix64 like irix. Fixes #764560. Will backport to 2.2.
diff --git a/configure.in b/configure.in
index 5e4be7a..16a1642 100644
--- a/configure.in
+++ b/configure.in
@@ -117,6 +117,7 @@
 	cygwin*) MACHDEP="cygwin";;
 	darwin*) MACHDEP="darwin";;
 	atheos*) MACHDEP="atheos";;
+        irix646) MACHDEP="irix6";;
 	'')	MACHDEP="unknown";;
 	esac
 fi