Driver: Add a --rtlib={compiler-rt,libgcc} argument which I plan to use to allow
dual support for compiler-rt on Linux, during bringup.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146094 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index fa4cf41..29559a6 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -440,6 +440,16 @@
 
 void DarwinClang::AddLinkRuntimeLibArgs(const ArgList &Args,
                                         ArgStringList &CmdArgs) const {
+  // Darwin only supports the compiler-rt based runtime libraries.
+  switch (GetRuntimeLibType(Args)) {
+  case ToolChain::RLT_CompilerRT:
+    break;
+  default:
+    getDriver().Diag(diag::err_drv_unsupported_rtlib_for_platform)
+      << Args.getLastArg(options::OPT_rtlib_EQ)->getValue(Args) << "darwin";
+    return;
+  }
+
   // Darwin doesn't support real static executables, don't link any runtime
   // libraries with -static.
   if (Args.hasArg(options::OPT_static))