Xcore target: Fix CXXStdlibIncludeArgs to check 'nostdinc++' flag too.

[robertlytton]

Summary

There are no tests as it is depenant upon the environment variables
XCC_C_INCLUDE_PATH & XCC_CPLUS_INCLUDE_PATH being set.

[• friedgold]

LGTM

[robertlytton]

Closed by commit rL214510 (authored by rlytton).

lib/Driver/ToolChains.cpp

 void XCore::addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                                      llvm::opt::ArgStringList &CC1Args) const {
   CC1Args.push_back("-nostdsysteminc");
 }
 
 void XCore::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
                                          ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdinc) ||
-      DriverArgs.hasArg(options::OPT_nostdlibinc))
+      DriverArgs.hasArg(options::OPT_nostdlibinc) ||
+      DriverArgs.hasArg(options::OPT_nostdincxx))
     return;
   if (const char *cl_include_dir = getenv("XCC_CPLUS_INCLUDE_PATH")) {
     SmallVector<StringRef, 4> Dirs;
     const char EnvPathSeparatorStr[] = {llvm::sys::EnvPathSeparator,'\0'};
     StringRef(cl_include_dir).split(Dirs, StringRef(EnvPathSeparatorStr));
     ArrayRef<StringRef> DirVec(Dirs);
     addSystemIncludes(DriverArgs, CC1Args, DirVec);
   }
 }
 
 void XCore::AddCXXStdlibLibArgs(const ArgList &Args,
                                 ArgStringList &CmdArgs) const {
   // We don't output any lib args. This is handled by xcc.
 }