This patch is in response to
<https://sourceware.org/ml/libc-alpha/2020-02/msg00625.html>

With this patch, branch tuliom/libmvec has all changes needed to
enable GCC to autovectorize libmvec functions. Other than sincos.
Getting GCC to vectorize sincos is work-in-progress; presently GCC
does NOT vectorize for any architecture.

Bert.