[modules] Don't leak -M flags for dependency file generation into the module

build process when we implicitly build a module. Previously, we'd create the
specified .d file once for each implicitly-built module and then finally
overwrite it with the correct contents after the requested build completes.
(This fails if you use stdout as a dependency file, which is what the provided
testcase does, and is how I discovered this brokenness.)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@244412 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Frontend/CompilerInstance.cpp

@@ -944,8 +944,10 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
     FullSourceLoc(ImportLoc, ImportingInstance.getSourceManager()));
 
   // If we're collecting module dependencies, we need to share a collector
-  // between all of the module CompilerInstances.
+  // between all of the module CompilerInstances. Other than that, we don't
+  // want to produce any dependency output from the module build.
   Instance.setModuleDepCollector(ImportingInstance.getModuleDepCollector());
+  Invocation->getDependencyOutputOpts() = DependencyOutputOptions();
 
   // Get or create the module map that we'll use to build this module.
   std::string InferredModuleMapContent;

test/Modules/dependency-gen.modulemap

 // RUN: cd %S
-// RUN: rm -f %t.cpm %t-base.pcm %t-base.d %t.d
-// RUN: %clang_cc1 -I. -x c++ -fmodule-name=test-base -fmodules -emit-module -fno-validate-pch -fmodules-strict-decluse Inputs/dependency-gen-base.modulemap -dependency-file %t-base.d -MT %t-base.pcm -o %t-base.pcm -fmodule-map-file-home-is-cwd
-// RUN: %clang_cc1 -I. -x c++ -fmodule-name=test -fmodules -emit-module -fno-validate-pch -fmodules-strict-decluse -fmodule-file=%t-base.pcm %s -dependency-file %t.d -MT %t.pcm -o %t.pcm -fmodules-cache-path=%t -fmodule-map-file-home-is-cwd
+// RUN: rm -rf %t
+//
+// RUN: %clang_cc1 -I. -x c++ -fmodule-name=test -fmodules -emit-module -fno-validate-pch -fmodules-strict-decluse %s -dependency-file - -MT implicit.pcm -o %t/implicit.pcm -fmodules-cache-path=%t -fmodule-map-file-home-is-cwd | FileCheck %s
+//
+// RUN: %clang_cc1 -I. -x c++ -fmodule-name=test-base -fmodules -emit-module -fno-validate-pch -fmodules-strict-decluse Inputs/dependency-gen-base.modulemap -o %t/base.pcm -fmodule-map-file-home-is-cwd
+// RUN: %clang_cc1 -I. -x c++ -fmodule-name=test -fmodules -emit-module -fno-validate-pch -fmodules-strict-decluse -fmodule-file=%t/base.pcm %s -dependency-file - -MT explicit.pcm -o %t/explicit.pcm -fmodules-cache-path=%t -fmodule-map-file-home-is-cwd | FileCheck %s
 // RUN: FileCheck %s < %t.d
 module "test" {
   export *