[Frontend] Remove unused FileMgr in pp arg parse

Summary:
A FIXME added 8 years ago (2010) in https://reviews.llvm.org/rL118203
mentioned that a FileManager should not need to be used when parsing
preprocessor arguments. In fact, its only use was removed 6 years ago
(2012), in https://reviews.llvm.org/rL166452. Remove the unused
variable and the obsolete FIXME.

Test Plan: `check-clang`

Reviewers: v.g.vassilev

Reviewed By: v.g.vassilev

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D41867

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@322118 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Frontend/CompilerInvocation.cpp

@@ -2618,7 +2618,6 @@ static bool isStrictlyPreprocessorAction(frontend::ActionKind Action) {
 }
 
 static void ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,
-                                  FileManager &FileMgr,
                                   DiagnosticsEngine &Diags,
                                   frontend::ActionKind Action) {
   using namespace options;
@@ -2840,12 +2839,7 @@ bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Res,
       !LangOpts.Sanitize.has(SanitizerKind::Address) &&
       !LangOpts.Sanitize.has(SanitizerKind::Memory);
 
-  // FIXME: ParsePreprocessorArgs uses the FileManager to read the contents of
-  // PCH file and find the original header name. Remove the need to do that in
-  // ParsePreprocessorArgs and remove the FileManager
-  // parameters from the function and the "FileManager.h" #include.
-  FileManager FileMgr(Res.getFileSystemOpts());
-  ParsePreprocessorArgs(Res.getPreprocessorOpts(), Args, FileMgr, Diags,
+  ParsePreprocessorArgs(Res.getPreprocessorOpts(), Args, Diags,
                         Res.getFrontendOpts().ProgramAction);
   ParsePreprocessorOutputArgs(Res.getPreprocessorOutputOpts(), Args,
                               Res.getFrontendOpts().ProgramAction);