Add more fma tests.

In my review
<https://sourceware.org/ml/libc-alpha/2018-06/msg00375.html> of a
patch for bug 23584, I expressed concern that the proposed changes
didn't deal with certain cases similar to the ones in the bug but
where test coverage was missing.

This patch adds such tests of fma (Inf, finite, finite) and fma
(finite, Inf, finite) to libm-test-fma.inc.  It does *not* do anything
to fix the bug, simply adds test coverage to provide stronger evidence
of whether any proposed revised fix does address the cases I was
concerned with.

Tested for x86_64 and x86.

	* math/libm-test-fma.inc (fma_test_data): Add more tests.