[clang][WebAssembly] Link with profile runtime libraries if requested

This patch teaches the WebAssembly toolchain to link with the profile
runtime libraries if profile instrumentation is requested. With this
change, the following command will work with profile rt installed:

```
$ clang -target wasm32-unknown-wasi -fprofile-instr-generate \
  -lwasi-emulated-getpid -lwasi-emulated-mman -o foo.wasm foo.c
```

clang/lib/Driver/ToolChains/WebAssembly.cpp

@@ -163,6 +163,8 @@ void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     AddRunTimeLibs(ToolChain, ToolChain.getDriver(), CmdArgs, Args);
   }
 
+  ToolChain.addProfileRTLibs(Args, CmdArgs);
+
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());