[Driver] Print path to correct rtlib for -print-libgcc-file-name

[phosek]

Summary

When compiler-rt is being used as a runtime library, Clang would print an invalid path when -print-libgcc-file-name option is used. We should print a path to compiler-rt builtin library instead.

[phosek]

Michał Górny has submitted the same change as D25338 and his change seems to be getting more traction.

lib/Driver/Driver.cpp

bool Driver::HandleImmediateArgs(const Compilation &C) {
   }
 
   if (Arg *A = C.getArgs().getLastArg(options::OPT_print_prog_name_EQ)) {
     llvm::outs() << GetProgramPath(A->getValue(), TC) << "\n";
     return false;
   }
 
   if (C.getArgs().hasArg(options::OPT_print_libgcc_file_name)) {
-    llvm::outs() << GetFilePath("libgcc.a", TC) << "\n";
+    ToolChain::RuntimeLibType RLT = TC.GetRuntimeLibType(C.getArgs());
+    std::string Path;
+    switch (RLT) {
+    case ToolChain::RLT_CompilerRT:
+      Path = TC.getCompilerRT(C.getArgs(), "builtins");
+      break;
+    case ToolChain::RLT_Libgcc:
+      Path = GetFilePath("libgcc.a", TC);
+      break;
+    }
+    llvm::outs() << Path << "\n";
     return false;
   }
 
   if (C.getArgs().hasArg(options::OPT_print_multi_lib)) {
     for (const Multilib &Multilib : TC.getMultilibs())
       llvm::outs() << Multilib << "\n";
     return false;
   }