libcxx: only pass -DHAVE___CXA_THREAD_ATEXIT_IMPL for glibc
This definition communicates to libcxxabi that the libc will provide the
`__cxa_thread_atexit_impl` symbol. This is true for glibc but not
true for other libcs, such as musl.
710e2e7f10Andrew Kelley committed on 10/27/2022, 5:03:11 AMparent0b72965