Target: Android: support exp10 now

Summary:
As of D178 we now support exp10, so let's take advantage of it by converting
pow(10.0,x) to the much faster and more inaccurate exp10(x).

Test Plan: verifying after D178 cleanup

Reviewers: randall.rushing, jriordan001, anders3408

Differential Revision: http://review.codefirex.com/D478