libm: optimistic pow calling.

Call optimized pow optimistically and revert to full range
implementation if we detect an out-of-range input.

Change-Id: I6f3aa734adbf99484b7ff70736ef83a41e5815b8
(cherry picked from commit e7fd29685a75f1d26061ac511e7a29479fd871b5)
(cherry picked from commit 7916899916973ca5695526ae45283e54709df32a)
(cherry picked from commit d39a7f744c78409949482e3cb3c9710e8f281a33)
3 files changed