Update libm tests from NetBSD

I did this without a full vendor update since that would cause too many
conflicts. Since these files now almost match the NetBSD sources the
next git subtree merge should work just fine.

Reviewed By: lwhsu
Differential Revision: https://reviews.freebsd.org/D28797

(cherry picked from commit 1ec3feb64826d2a43d41e74684690985bf20e71c)