Fix ldbl-128 / ldbl-128ibm lgammal spurious underflow (bug 16400).

Fix ldbl-128 / ldbl-128ibm lgammal spurious underflow (bug 16400).

This patch fixes bug 16400, spurious underflow exceptions for ldbl-128
/ ldbl-128ibm lgammal with small positive arguments, by just using
-__logl (x) as the result in the problem cases (similar to the
previous fix for problems with small negative arguments).

Tested powerpc32, and also tested on mips64 that this does not require
ulps regeneration for the ldbl-128 case.

	* sysdeps/ieee754/ldbl-128/e_lgammal_r.c (__ieee754_lgammal_r):
	Return -__logl (x) for small positive arguments without evaluating
	a polynomial.