fortran: Teach get_real_kind_from_node for Power 128 fp modes [PR112993]

fortran: Teach get_real_kind_from_node for Power 128 fp modes [PR112993]

Previously effective target fortran_real_c_float128 never
passes on Power regardless of the default 128 long double
is ibmlongdouble or ieeelongdouble.  It's due to that TF
mode is always used for kind 16 real, which has precision
127, while the node float128_type_node for c_float128 has
128 type precision, get_real_kind_from_node can't find a
matching as it only checks gfc_real_kinds[i].mode_precision
and type precision.

With changing TFmode/IFmode/KFmode to have the same mode
precision 128, now fortran_real_c_float12 can pass with
ieeelongdouble enabled by default and test cases guarded
with it get tested accordingly.  But with ibmlongdouble
enabled by default, since TFmode has precision 128 which
is the same as type precision 128 of float128_type_node,
get_real_kind_from_node considers kind for TFmode matches
float128_type_node, but it's wrong as at this time point
TFmode is with ibm extended format.  So this patch is to
teach get_real_kind_from_node to check one more field which
can be differentiable from the underlying real format, it
can avoid the unexpected matching when there more than one
modes have the same precisoin.

	PR target/112993

gcc/fortran/ChangeLog:

	* trans-types.cc (get_real_kind_from_node): Consider the case where
	more than one modes have the same precision.