[Driver] Use stem rather than filename for executable name

[phosek]

Summary

When comparing the linker name in Fuchsia driver, use stem rather than filename to get the name of the linker becase on Windows, the filename will have an extension.

[bruno]

Can you add a testcase for that?

[davide]

Was going to commit the same. Thanks. LGTM.

[davide]

And yes, if you can add a test case that will be great (there's no bot that caught this upstream) but one of our internal bots did.

[phosek]

In D25700#572158, @bruno wrote:

Can you add a testcase for that?

This is already covered by an existing testcase which was failing on Windows (davide pointed that out to me).

[bruno]

Ok, thanks! LGTM

cfe/trunk/lib/Driver/Tools.cpp

void fuchsia::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   Args.ClaimAllArgs(options::OPT_g_Group);
   // and "clang -emit-llvm foo.o -o foo"
   Args.ClaimAllArgs(options::OPT_emit_llvm);
   // and for "clang -w foo.o -o foo". Other warning options are already
   // handled somewhere else.
   Args.ClaimAllArgs(options::OPT_w);
 
   const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath());
-  if (llvm::sys::path::filename(Exec).equals_lower("lld")) {
+  if (llvm::sys::path::stem(Exec).equals_lower("lld")) {
     CmdArgs.push_back("-flavor");
     CmdArgs.push_back("gnu");
   }
 
   if (!D.SysRoot.empty())
     CmdArgs.push_back(Args.MakeArgString("--sysroot=" + D.SysRoot));
 
   if (!Args.hasArg(options::OPT_shared) && !Args.hasArg(options::OPT_r))