When compiling on aarch64 some `LDBL_MANT_DIG == 113` entries
end up trying to use `complex<long double>` for which there are
no certain specializations in `libcudacxx`. This change-set
includes a clean-up for `LDBL_MANT_DIG == 113` usage, which is replaced
with `HAS_LDBL128` that is set in `float128.h`.
This PR does not include support for COMPLEX(16) intrinsics.
Note that (fp ** int) operations do not require Float128Math library,
as they are implemented via basic F128 operations,
which are supported by the build compilers' runtimes.