Add option to disable module loading.

This patch was created by Lawrence Crowl and reviewed in:
http://llvm-reviews.chandlerc.com/D963

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187738 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index dfaffaa..254bf8b 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -3070,6 +3070,13 @@
     }
   }
 
+  // -fmodule-maps enables module map processing (off by default) for header
+  // checking.  It is implied by -fmodules.
+  if (Args.hasFlag(options::OPT_fmodule_maps, options::OPT_fno_module_maps,
+                   false)) {
+    CmdArgs.push_back("-fmodule-maps");
+  }
+
   // If a module path was provided, pass it along. Otherwise, use a temporary
   // directory.
   if (Arg *A = Args.getLastArg(options::OPT_fmodules_cache_path)) {