[compiler-rt][CMake] Remove unused -stdlib when passing -nostdinc++

We added -nostdinc++ to clang_rt.profile in https://reviews.llvm.org/D84205.
This will cause warnings when building with LLVM_ENABLE_LIBCXX,
and failure if with Werror on.

This patch is to fix it by removing unused -stdlib,
similar to what we have done in https://reviews.llvm.org/D42238.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D84543