Fix test on Windows

'not' on Windows tries and fails to convert the argument to UTF-16 and back for
some reason:

  Error: Unable to convert command-line to UTF-16

Let's try replacing it with !.

(There was no obvious way to do these with FileCheck)

llvm-svn: 195907

clang/test/Frontend/rewrite-includes-bom.c

@@ -1,6 +1,6 @@
-// RUN: grep $'^\xEF\xBB\xBF' %S/Inputs/rewrite-includes-bom.h
+// RUN: grep -q $'^\xEF\xBB\xBF' %S/Inputs/rewrite-includes-bom.h
 // RUN: %clang_cc1 -E -frewrite-includes -I %S/Inputs %s -o %t.c
-// RUN: not grep $'\xEF\xBB\xBF' %t.c
+// RUN: ! grep -q $'\xEF\xBB\xBF' %t.c
 // RUN: %clang_cc1 -fsyntax-only -verify %t.c
 // expected-no-diagnostics
 // REQUIRES: shell