Revert "Revert "[libportable] Add fenv support.""

This reverts commit 366a681cefd44a354bc3b47ca6a12f0b1b67aee3.

Conflicts:
	ndk/sources/android/libportable/Android.mk

Change-Id: I3cae2ceef599acffa29f03fea6b0f5167d722b1a