For NetBSD/current on X86 do not use libgcc and default to libc++.
Adjust linkage to make more sense for older releases.

llvm-svn: 192615
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index a2e64f2..ec0d8f3 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -1982,6 +1982,12 @@
       << A->getAsString(Args);
   }
 
+  unsigned Major, Minor, Micro;
+  getTriple().getOSVersion(Major, Minor, Micro);
+  if (Major >= 7 || (Major == 6 && Minor == 99 && Micro >= 23) || Major == 0) {
+    if (getArch() == llvm::Triple::x86 || getArch() == llvm::Triple::x86_64)
+      return ToolChain::CST_Libcxx;
+  }
   return ToolChain::CST_Libstdcxx;
 }