[Caching] Use subInvocation to verify interface

The interface verification needs to read some command-line from the
interface file so it needs to be built inside sub-invocation.

rdar://122423965

Author: cachemeifyoucan

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -2043,8 +2043,6 @@ InterfaceSubContextDelegateImpl::runInSubCompilerInstance(StringRef moduleName,
   info.Instance = &subInstance;
   info.CompilerVersion = interfaceInfo.CompilerVersion;
 
-  subInstance.getSourceMgr().setFileSystem(SM.getFileSystem());
-
   ForwardingDiagnosticConsumer FDC(*Diags);
   NullDiagnosticConsumer noopConsumer;
   if (!silenceErrors) {
@@ -2053,11 +2051,19 @@ InterfaceSubContextDelegateImpl::runInSubCompilerInstance(StringRef moduleName,
     subInstance.addDiagnosticConsumer(&noopConsumer);
   }
 
+  // If doing typecheck, emit warnings.
+  if (subInvocation.getFrontendOptions().isTypeCheckAction())
+    subInvocation.getDiagnosticOptions().SuppressWarnings = false;
+
   std::string InstanceSetupError;
   if (subInstance.setup(subInvocation, InstanceSetupError)) {
     return std::make_error_code(std::errc::not_supported);
   }
 
+  // Set the file system after setup to make sure the file system is shared in
+  // subInstance.
+  subInstance.getSourceMgr().setFileSystem(SM.getFileSystem());
+
   info.BuildArguments = BuildArgs;
   info.Hash = CacheHash;
   auto target = *(std::find(BuildArgs.rbegin(), BuildArgs.rend(), "-target") - 1);

lib/FrontendTool/FrontendTool.cpp

@@ -418,9 +418,7 @@ static bool buildModuleFromInterface(CompilerInstance &Instance) {
   // currently we need to ensure it still reads the flags written out
   // in the .swiftinterface file itself. Instead, creation of that
   // job should incorporate those flags.
-  if (FEOpts.ExplicitInterfaceBuild &&
-      !(FEOpts.isTypeCheckAction() &&
-        !Invocation.getCASOptions().EnableCaching))
+  if (FEOpts.ExplicitInterfaceBuild && !(FEOpts.isTypeCheckAction()))
     return ModuleInterfaceLoader::buildExplicitSwiftModuleFromSwiftInterface(
         Instance, Invocation.getClangModuleCachePath(),
         FEOpts.BackupModuleInterfaceDir, PrebuiltCachePath, ABIPath, InputPath,