[clang] Allow the OpenBSD driver to link the libclang_rt.profile library.

[fcambus]

Summary

With this change, passing -fprofile-instr-generate -fcoverage-mapping
when building programs will attempt linking against libclang_rt.profile.

[MaskRay]

Without testing libclang_rt.profile{{.*}}.a in clang/test/Driver, such functionality may regress.
If I am to refactor addProfileRTLibs, I may not notice the untested feature.

clang/lib/Driver/ToolChains/OpenBSD.cpp

if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles)) {
     if (!Args.hasArg(options::OPT_shared))
       crtend = "crtend.o";
     else
       crtend = "crtendS.o";
 
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtend)));
   }
 
+  ToolChain.addProfileRTLibs(Args, CmdArgs);
+
   const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath());
   C.addCommand(std::make_unique<Command>(JA, *this,
                                          ResponseFileSupport::AtFileCurCP(),
                                          Exec, CmdArgs, Inputs, Output));
 }
 
 SanitizerMask OpenBSD::getSupportedSanitizers() const {
   const bool IsX86 = getTriple().getArch() == llvm::Triple::x86;