Fix ldbl-128 log1pl (-qNaN) spurious "invalid" exception (bug 19189).

Fix ldbl-128 log1pl (-qNaN) spurious "invalid" exception (bug 19189).

The ldbl-128 version of log1pl raises a spurious "invalid" exception
for a -qNaN argument.  This patch fixes this by making the initial
check for infinities and NaNs handle arguments of both signs in such a
way that NaNs result in a NaN being returned (quietly if the input NaN
was quiet) while +Inf results in +Inf being returned and -Inf results
in a qNaN being returned with "invalid" exception raised.

Tested for mips64.

	[BZ #19189]
	* sysdeps/ieee754/ldbl-128/s_log1pl.c (__log1pl): Make check for
	non-finite argument handle arguments with negative sign.