Use -fno-math-errno for libm

This option allows inline calls of single intructions if target,
supports it.  Currently it optimizes internal sqrt calls on
armeabi-v7a, arm64-v8a, and x86_64 (by removing internal calls
to sqrt).

Test: Builds, ran unit tests on arm and x86.

Change-Id: I8a7621a55aae82ff5b80e886c9ed49d480ef6263