Issue #1633863: Don't ignore $CC under AIX.
diff --git a/configure.in b/configure.in
index c6a51a3..d9e208e 100644
--- a/configure.in
+++ b/configure.in
@@ -449,7 +449,7 @@
 		without_gcc=$withval;;
 	esac], [
 	case $ac_sys_system in
-	AIX*)   CC=cc_r
+	AIX*)   CC=${CC:-xlc_r}
 		without_gcc=;;
 	*)	without_gcc=no;;
 	esac])