Fix verify-broken-c-module to work on macOS.

Shorten expected error message so that it doesn't expect "C module" (and
breaks if presented with "Objective-C module").

Author: martinboehme

test/Frontend/verify-broken-c-module.swift

@@ -5,7 +5,7 @@
 
 // RUN: not %target-typecheck-verify-swift -I %S/Inputs/broken-c-module 2>&1 | %FileCheck %s
 
-// CHECK: [[@LINE+3]]:8: error: unexpected error produced: could not build C module 
+// CHECK: [[@LINE+3]]:8: error: unexpected error produced: could not build
 // CHECK: note: in file included from <module-includes>
 // CHECK: broken_c.h:2:11: error: expected function body after function declarator
 import BrokenCModule