Fix gen-tgmath-tests.py for _Float64, _Float64x testing.

Fix gen-tgmath-tests.py for _Float64, _Float64x testing.

math/gen-tgmath-tests.py was missing a create_type argument when
creating the internal types for combinations of long double with
_Float64 and _Float64x, so resulting in output that did not compile
when glibc support for those types was enabled.  This patch adds the
missing argument so that the tests properly compile in that case.

Tested for x86_64, including in conjunction with _Float64x support
patches.

	* math/gen-tgmath-tests.py (Type.init_types): Pass suffix argument
	for combinations of long double with _Float64 and _Float64x.