Remove Driver::UseStdLib.

All but one place are checking options::OPT_nostdlib instead of looking at
this field, so convert that one other place to doing that as well.

No behavior change.

llvm-svn: 308848
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 98b0bda..361d45f 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -87,7 +87,7 @@
     : Opts(createDriverOptTable()), Diags(Diags), VFS(std::move(VFS)),
       Mode(GCCMode), SaveTemps(SaveTempsNone), BitcodeEmbed(EmbedNone),
       LTOMode(LTOK_None), ClangExecutable(ClangExecutable),
-      SysRoot(DEFAULT_SYSROOT), UseStdLib(true),
+      SysRoot(DEFAULT_SYSROOT), 
       DriverTitle("clang LLVM compiler"), CCPrintOptionsFilename(nullptr),
       CCPrintHeadersFilename(nullptr), CCLogDiagnosticsFilename(nullptr),
       CCCPrintBindings(false), CCPrintHeaders(false), CCLogDiagnostics(false),
@@ -678,8 +678,6 @@
     SysRoot = A->getValue();
   if (const Arg *A = Args.getLastArg(options::OPT__dyld_prefix_EQ))
     DyldPrefix = A->getValue();
-  if (Args.hasArg(options::OPT_nostdlib))
-    UseStdLib = false;
 
   if (const Arg *A = Args.getLastArg(options::OPT_resource_dir))
     ResourceDir = A->getValue();