Fix ldbl-128 logl for subnormals (bug 16338).

Fix ldbl-128 logl for subnormals (bug 16338).

This patch fixes bug 16338, ldbl-128 logl not handling subnormals
(with consequent inaccuracy for lgammal as well).  The fix is simply
to use __frexpl when determining the exponent, as done already in
log2l and log10l.  Given the lack of testing of small arguments to any
of the log* functions, appropriate tests are added for all of them.

Tested x86_64 and x86 and ulps updated accordingly, and spot tests
also run for mips64 to confirm the ldbl-128 fix.

Note that while this fixes lgammal inaccuracy for small positive
arguments, I suspect that there will still be problems with spurious
underflows in that case.

	* sysdeps/ieee754/ldbl-128/e_logl.c (__ieee754_logl): Use __frexpl
	to determine exponent and adjust argument to have exponent of -1.
	* math/auto-libm-test-in: Add more tests of log, log10, log1p and
	log2.
	* math/auto-libm-test-out: Regenerated.
	* sysdeps/x86_64/fpu/libm-test-ulps: Update.