Un-split hypot<long double> tests

Un-split hypot<long double> tests

Remove the hypot-long-double.cc file that used dg-xfail-run-if and
simply use the lower tolerance for double if long double is not larger
than double.

	* testsuite/26_numerics/headers/cmath/hypot-long-double.cc: Remove.
	* testsuite/26_numerics/headers/cmath/hypot.cc: Restore test for
	long double unconditionally, but use lower tolerance when
	sizeof(long double) == sizeof(double).

From-SVN: r264483