[WebAssembly] Fix location and -flavor when running lld

[sbc100]

Summary

Add the toolchain installation directory to the program
path so that lld can be found.

Update -flavor to be wasm. Although this new flavor
hasn't yet landed in upstream lld yet there are no point
in passing wasm objects the gnu flavor.

[pcc]

Hi Sam, just out of curiosity, are there any details available about your plans for the wasm port of lld? I couldn't seem to find any by searching the lists.

[sbc100]

Hi Peter. I've been doing some preliminary work which is currently here: https://github.com/sbc100/lld/tree/add_wasm_linker_skeleton

I have been meaning to send out a message about this work to the mailing list, and this is probably good time to do that. As soon as the prototype is able to link basic single-file programs I was hoping to try and get it merged upstream. There is a general lack of a real linker story in the wasm world right now and lld seemed like to good place to build one.

cfe/trunk/lib/Driver/ToolChains/WebAssembly.cpp

void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                 const ArgList &Args,
                                 const char *LinkingOutput) const {
 
   const ToolChain &ToolChain = getToolChain();
   const Driver &D = ToolChain.getDriver();
   const char *Linker = Args.MakeArgString(ToolChain.GetLinkerPath());
   ArgStringList CmdArgs;
   CmdArgs.push_back("-flavor");
-  CmdArgs.push_back("ld");
+  CmdArgs.push_back("wasm");
 
   // Enable garbage collection of unused input sections by default, since code
   // size is of particular importance. This is significantly facilitated by
   // the enabling of -ffunction-sections and -fdata-sections in
   // Clang::ConstructJob.
   if (areOptimizationsEnabled(Args))
     CmdArgs.push_back("--gc-sections");
 
void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   C.addCommand(llvm::make_unique<Command>(JA, *this, Linker, CmdArgs, Inputs));
 }
 
 WebAssembly::WebAssembly(const Driver &D, const llvm::Triple &Triple,
                          const llvm::opt::ArgList &Args)
   : ToolChain(D, Triple, Args) {
 
   assert(Triple.isArch32Bit() != Triple.isArch64Bit());
+
+  getProgramPaths().push_back(getDriver().getInstalledDir());
+
   getFilePaths().push_back(
       getDriver().SysRoot + "/lib" + (Triple.isArch32Bit() ? "32" : "64"));
 }
 
 bool WebAssembly::IsMathErrnoDefault() const { return false; }
 
 bool WebAssembly::IsObjCNonFragileABIDefault() const { return true; }