libm: sync with upstream freebsd

Summary:
New long double functions have been included,
but are not in use due to the android double long
handling. imprecise.c is not built for the same reason.

Test Plan: verified

Reviewers: randall.rushing

Differential Revision: http://review.codefirex.com/D232

Change-Id: I77f2b6e202dd500ed38d62edf187a5ac10b3002c
Signed-off-by: DHOMD <DHO@dho.im>
libm: add fmal long double stub

Summary:
This is needed in some target cases, and has since been fixed internally in the AOSP.

From enh@google.com regarding this change:
you were right, and this was the way we should have done it, but i didn't work that out until i fixed this in the same way as part of the aarch64 work (where the weak reference didn't work).

Test Plan: verified

Reviewers: randall.rushing, jriordan001, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D234

Change-Id: Ia57674b89e110a7fff4a90c534f67a6bbef57c68
Signed-off-by: DHOMD <DHO@dho.im>