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>