Frontend: Remove redundant call to CompilerInstance::setFileManager, NFC

[dexonsmith]

Summary

ASTUnit::Parse sets up the FileManager earlier in the same function,
ensuring ASTUnit::getFileManager() matches Clang->getFileManager().
Remove the later call to setFileManager(getFileManager()) since it
does nothing.

[dexonsmith]

clang/lib/Frontend/ASTUnit.cpp

1135–1141

Here's where the FileManager was already set up.

[dexonsmith]

ping

[jansvoboda11]

LGTM

clang/lib/Frontend/ASTUnit.cpp

auto CleanOnError = llvm::make_scope_exit([&]() {
     // Keep the ownership of the data in the ASTUnit because the client may
     // want to see the diagnostics.
     transferASTDataFromCompilerInstance(*Clang);
     FailedParseDiagnostics.swap(StoredDiagnostics);
     StoredDiagnostics.clear();
     NumStoredDiagnosticsFromDriver = 0;
   });
 
   // Ensure that Clang has a FileManager with the right VFS, which may have
   // changed above in AddImplicitPreamble.  If VFS is nullptr, rely on
   // createFileManager to create one.
   if (VFS && FileMgr && &FileMgr->getVirtualFileSystem() == VFS)
     Clang->setFileManager(&*FileMgr);
   else
     FileMgr = Clang->createFileManager(std::move(VFS));
 
   // Recover resources if we crash before exiting this method.
   llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance>
     CICleanup(Clang.get());
 
   Clang->setInvocation(CCInvocation);
   OriginalSourceFile =
       std::string(Clang->getFrontendOpts().Inputs[0].getFile());
bool ASTUnit::Parse(std::shared_ptr<PCHContainerOperations> PCHContainerOps,
 
   SourceMgr = new SourceManager(getDiagnostics(), *FileMgr,
                                 UserFilesAreVolatile);
   if (!OverrideMainBuffer) {
     checkAndRemoveNonDriverDiags(StoredDiagnostics);
     TopLevelDeclsInPreamble.clear();
   }
 
-  // Create a file manager object to provide access to and cache the filesystem.
-  Clang->setFileManager(&getFileManager());
-
   // Create the source manager.
   Clang->setSourceManager(&getSourceManager());
 
   // If the main file has been overridden due to the use of a preamble,
   // make that override happen and introduce the preamble.
   if (OverrideMainBuffer) {
     // The stored diagnostic has the old source manager in it; update
     // the locations to refer into the new source manager. Since we've