Update MIPS math-tests.h for GCC 4.9 using soft-fp.

GCC trunk now uses soft-fp for MIPS64 long double, so supporting
integration with hardware exceptions and rounding modes.  This patch
updates MIPS math-tests.h accordingly not to disable exception and
rounding mode tests in this case.

Tested mips64 and ulps updated to reflect the newly run tests.

	* sysdeps/mips/math-tests.h: Include <features.h>.
	[!__mips_soft_float && _MIPS_SIM != _ABIO32 && __GNUC_PREREQ (4, 9)]
	(ROUNDING_TESTS_long_double): Do not define.
	[!__mips_soft_float && _MIPS_SIM != _ABIO32 && __GNUC_PREREQ (4, 9)]
	(EXCEPTION_TESTS_long_double): Likewise.
	* sysdeps/mips/mips64/libm-test-ulps: Update.