[libc++abi] Provide __cxa_thread_atexit on Fuchsia

Fuchsia already supports this interface.

Differential Revision: https://reviews.llvm.org/D53801

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@345534 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed