clang/test/Driver/working-directory.c: Exclude msys bash rather than tweaking expressions.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189927 91177308-0d34-0410-b5e6-96231b3b80d8

test/Driver/working-directory.c

 // RUN: %clang -### -working-directory /no/such/dir/ input 2>&1 | FileCheck %s
+// REQUIRES: shell-preserves-root
 
 //CHECK: no such file or directory: '/no/such/dir/input'