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

Don't expect :fmod to fail on FreeBSD

Sponsored by: EMC / Isilon Storage Division

The fmodl compat shims on arm/mips/powerpc aren't complete

Disable the test code for now on those architectures

MFC after: 1 week
PR: 199422