[compiler-rt] Fix test failures when switching default C++ library

1. Add two explicit -stdlib=libstdc++ in conjunction with -static-libstdc++
2. Pass -nostdinc++ when adding include paths for libc++ built for tsan. This
   prevents clang finding the headers twice which would confuse #include_next

Differential Revision: http://reviews.llvm.org/D17189

llvm-svn: 260883