Add an overload to ASTUnit::LoadFromASTFile that accepts a virtual file system.

[ymandel]

Why add an overload rather than adding it before UseDebugInfo and defaulting it to getRealFileSystem()?

[ymandel]

To be clear, I'm fine with the change either way, just want to understand a bit better first.

[asoffer]

Use default arguments instead of overloads.

[asoffer]

I don't know what happened here, but when I update a diff half my changes disappear. I'm going to recreate this in a new diff.

clang/lib/Frontend/ASTUnit.cpp

std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
   }
 
   // Tell the diagnostic client that we have started a source file.
   AST->getDiagnostics().getClient()->BeginSourceFile(PP.getLangOpts(), &PP);
 
   return AST;
 }
 
-std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
-    const std::string &Filename, const PCHContainerReader &PCHContainerRdr,
-    WhatToLoad ToLoad, IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
-    const FileSystemOptions &FileSystemOpts, bool UseDebugInfo,
-    bool OnlyLocalDecls, CaptureDiagsKind CaptureDiagnostics,
-    bool AllowASTWithCompilerErrors, bool UserFilesAreVolatile) {
-  return LoadFromASTFile(Filename, PCHContainerRdr, ToLoad, Diags,
-                         llvm::vfs::getRealFileSystem(), FileSystemOpts,
-                         UseDebugInfo, OnlyLocalDecls, CaptureDiagnostics,
-                         AllowASTWithCompilerErrors, UserFilesAreVolatile);
-}
-
 /// Add the given macro to the hash of all top-level entities.
 static void AddDefinedMacroToHash(const Token &MacroNameTok, unsigned &Hash) {
   Hash = llvm::djbHash(MacroNameTok.getIdentifierInfo()->getName(), Hash);
 }
 
 namespace {
 
 /// Preprocessor callback class that updates a hash value with the names