clang/test/Driver: Introduce the feature "clang-driver", set if gcc driver is not used.

It is not set at targetting cygming. See PR12920.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169824 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Driver/debug-options-as.c b/test/Driver/debug-options-as.c
index 57036e4..20e104e 100644
--- a/test/Driver/debug-options-as.c
+++ b/test/Driver/debug-options-as.c
@@ -1,5 +1,5 @@
 // cygming have not supported integrated-as yet.
-// XFAIL: cygwin,mingw32
+// REQUIRES: clang-driver
 //
 // Check to make sure clang is somewhat picky about -g options.
 // (Delived from debug-options.c)