[NFC] Refactor ExecuteAssembler in cc1as_main.cpp

[scott.linder]

Summary

Introduce an extra scope (another static function) to replace calls to
unique_ptr::reset with implicit destructors via RAII.

[scott.linder]

I'm not sure who else to add, please feel free to update the reviewers

[MaskRay]

Seems reasonable.

clang/tools/driver/cc1as_main.cpp

getOutputStream(StringRef Path, DiagnosticsEngine &Diags, bool Binary) {
   if (EC) {
     Diags.Report(diag::err_fe_unable_to_open_output) << Path << EC.message();
     return nullptr;
   }
 
   return Out;
 }
 
-static bool ExecuteAssembler(AssemblerInvocation &Opts,
+static bool ExecuteAssemblerImpl(AssemblerInvocation &Opts,
                                  DiagnosticsEngine &Diags) {
   // Get the target specific parser.
   std::string Error;
   const Target *TheTarget = TargetRegistry::lookupTarget(Opts.Triple, Error);
   if (!TheTarget)
     return Diags.Report(diag::err_target_unknown_triple) << Opts.Triple;
 
   ErrorOr<std::unique_ptr<MemoryBuffer>> Buffer =
       MemoryBuffer::getFileOrSTDIN(Opts.InputFile, /*IsText=*/true);
for (auto &S : Opts.SymbolDefs) {
     Ctx.setSymbolValue(Parser->getStreamer(), Sym, Value);
   }
 
   if (!Failed) {
     Parser->setTargetParser(*TAP.get());
     Failed = Parser->Run(Opts.NoInitialTextSection);
   }
 
-  // Parser has a reference to the output stream (Str), so close Parser first.
-  Parser.reset();
-  Str.reset();
-  // Close the output stream early.
-  BOS.reset();
-  FDOS.reset();
+  return Failed;
+}
+
+static bool ExecuteAssembler(AssemblerInvocation &Opts,
+                             DiagnosticsEngine &Diags) {
+  bool Failed = ExecuteAssemblerImpl(Opts, Diags);
 
   // Delete output file if there were errors.
   if (Failed) {
     if (Opts.OutputPath != "-")
       sys::fs::remove(Opts.OutputPath);
     if (!Opts.SplitDwarfOutput.empty() && Opts.SplitDwarfOutput != "-")
       sys::fs::remove(Opts.SplitDwarfOutput);
   }