Fix x86 / x86_64 expl, exp10l missing underflows (bug 16361).

Fix x86 / x86_64 expl, exp10l missing underflows (bug 16361).

Similar to various other bugs in this area, the x86 and x86_64
implementations of expl / exp10l can fail to produce underflow
exceptions when the unscaled result has trailing 0 bits so the scaling
down to subnormal precision is exact.  This patch fixes this by
forcing the exception in the case of tiny results.

Tested for x86_64 and x86.

	[BZ #16361]
	* sysdeps/i386/fpu/e_expl.S [!USE_AS_EXPM1L] (cmin): New object.
	[!USE_AS_EXPM1L] (IEEE754_EXPL): Force underflow exception for
	tiny results.
	* sysdeps/x86_64/fpu/e_expl.S [!USE_AS_EXPM1L] (cmin): New object.
	[!USE_AS_EXPM1L] (IEEE754_EXPL): Force underflow exception for
	tiny results.
	* math/auto-libm-test-in: Add more tests of exp and exp10.  Do not
	mark underflow exceptions as possibly missing for bug 16361.
	* math/auto-libm-test-out: Regenerated.