Add basic tests for the remaining 9 libm <fenv.h> functions.

It seems that feenableexcept/fegetexcept are lying to us on arm/arm64
because the hardware doesn't actually support such functionality. When
I get confirmation of that from ARM I'll fix the <fenv.h> implementation
correspondingly --- writing to/reading from reserved FP control register
bits as we currently do doesn't seem like the best of ideas.

Bug: http://b/31742322
Test: ran tests on arm/arm64/x86/x86-64
Change-Id: If78f83ddab221b568fa168c3364a7ae95c024983