[ASan] Don't link against libc++abi when not using libc++

This is a follow-up to r233860 which added -lc++abi when using ASan
on Mac, and broke Chromium's ASan build which doesn't use libc++.

llvm-svn: 234521
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index 9864d19..434dc4d 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -338,9 +338,12 @@
                                     OS + "_dynamic.dylib").str(),
                     /*AlwaysLink*/ true, /*IsEmbedded*/ false,
                     /*AddRPath*/ true);
-  // Add explicit dependcy on -lc++abi, as -lc++ doesn't re-export
-  // all RTTI-related symbols that UBSan uses.
-  CmdArgs.push_back("-lc++abi");
+
+  if (GetCXXStdlibType(Args) == ToolChain::CST_Libcxx) {
+    // Add explicit dependcy on -lc++abi, as -lc++ doesn't re-export
+    // all RTTI-related symbols that UBSan uses.
+    CmdArgs.push_back("-lc++abi");
+  }
 }
 
 void DarwinClang::AddLinkRuntimeLibArgs(const ArgList &Args,