[clang] Load -fembed-offload-object= through the VFS (llvm#160906)

This PR loads the path from `-fembed-offload-object=<path>` through the
VFS rather than going straight to the real file system. This matches the
behavior of other input files of the compiler. This technically changes
behavior in that `-fembed-offload-object=-` no longer loads the file
from stdin, but I don't think that was the intention of the original
code anyways.

Author: jansvoboda11

clang/include/clang/CodeGen/BackendUtil.h

@@ -49,7 +49,7 @@ void EmbedBitcode(llvm::Module *M, const CodeGenOptions &CGOpts,
                   llvm::MemoryBufferRef Buf);
 
 void EmbedObject(llvm::Module *M, const CodeGenOptions &CGOpts,
-                 DiagnosticsEngine &Diags);
+                 llvm::vfs::FileSystem &VFS, DiagnosticsEngine &Diags);
 } // namespace clang
 
 #endif

clang/lib/CodeGen/BackendUtil.cpp

@@ -1476,13 +1476,13 @@ void clang::EmbedBitcode(llvm::Module *M, const CodeGenOptions &CGOpts,
 }
 
 void clang::EmbedObject(llvm::Module *M, const CodeGenOptions &CGOpts,
-                        DiagnosticsEngine &Diags) {
+                        llvm::vfs::FileSystem &VFS, DiagnosticsEngine &Diags) {
   if (CGOpts.OffloadObjects.empty())
     return;
 
   for (StringRef OffloadObject : CGOpts.OffloadObjects) {
     llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> ObjectOrErr =
-        llvm::MemoryBuffer::getFileOrSTDIN(OffloadObject);
+        VFS.getBufferForFile(OffloadObject);
     if (ObjectOrErr.getError()) {
       auto DiagID = Diags.getCustomDiagID(DiagnosticsEngine::Error,
                                           "could not open '%0' for embedding");

clang/lib/CodeGen/CodeGenAction.cpp

@@ -1141,7 +1141,8 @@ void CodeGenAction::ExecuteAction() {
     TheModule->setTargetTriple(Triple(TargetOpts.Triple));
   }
 
-  EmbedObject(TheModule.get(), CodeGenOpts, Diagnostics);
+  EmbedObject(TheModule.get(), CodeGenOpts, CI.getVirtualFileSystem(),
+              Diagnostics);
   EmbedBitcode(TheModule.get(), CodeGenOpts, *MainFile);
 
   LLVMContext &Ctx = TheModule->getContext();

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1556,7 +1556,7 @@ void CodeGenModule::Release() {
   EmitBackendOptionsMetadata(getCodeGenOpts());
 
   // If there is device offloading code embed it in the host now.
-  EmbedObject(&getModule(), CodeGenOpts, getDiags());
+  EmbedObject(&getModule(), CodeGenOpts, *getFileSystem(), getDiags());
 
   // Set visibility from DLL storage class
   // We do this at the end of LLVM IR generation; after any operation