clang/test/Driver/cl.c: Don't attempt slash switches on msys bash.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187337 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Driver/cl.c b/test/Driver/cl.c
index 677ccac..1187a31 100644
--- a/test/Driver/cl.c
+++ b/test/Driver/cl.c
@@ -22,3 +22,6 @@
 // are not available in clang-cl.
 // DEFAULT: -fapple-kext
 // CL-NOT: -fapple-kext
+
+// Don't attempt slash switches on msys bash.
+// REQUIRES: shell-preserves-root