Mark more libm tests with xfail-rounding:ldbl-128ibm.

This patch marks more libm tests as expected to fail for ldbl-128ibm
in non-default rounding modes.  Given this, my expm1l fix
<https://sourceware.org/ml/libc-alpha/2014-01/msg00135.html> and my
libgcc fix <http://gcc.gnu.org/ml/gcc-patches/2014-01/msg00157.html>
for spurious overflows, the remaining failures in test-ldouble.out
(for powerpc32 hard float) are small ulps, spurious underflow and
inexact exceptions (the former probably arising from libgcc bugs
though I haven't checked each case; the latter are barely meaningful
for this format anyway when basic arithmetic isn't correctly rounding,
though most of them are probably GCC bug 59412 which doesn't actually
involve long double), missing underflow exceptions from clog, ctan and
ctanh (probably one of the known bugs for another function), and logb
in round-downward mode (bug 887, though it's really a GCC bug that
we're not currently working around).

Tested for powerpc32 hard float.

	* math/auto-libm-test-in: Mark various tests with
	xfail-rounding:ldbl-128ibm.
	* math/auto-libm-test-out: Regenerated.