PR fortran/96613,96686 - Fix type/kind issues, temporaries evaluating MIN/MAX

PR fortran/96613,96686 - Fix type/kind issues, temporaries evaluating MIN/MAX

When evaluating functions of the MIN/MAX variety inline, use a temporary
of appropriate type and kind, and convert to the result type at the end.
In the case of allowing for the GNU extensions to MIN/MAX, derive the
result kind consistently during simplificaton.

Furthermore, the Fortran standard requires type and kind of arguments to
the MIN/MAX intrinsics to all have the same type and kind.  While a GNU
extension accepts kind differences for integer and real arguments which
seems to have been used in legacy code, there is no reason to allow
different character kinds.  We now reject the latter unconditionally.

gcc/fortran/ChangeLog:

	* check.c (check_rest): Reject MIN/MAX character arguments of
	different kind.
	* simplify.c (min_max_choose): The simplification result shall
	have the highest kind value of the arguments.
	* trans-intrinsic.c (gfc_conv_intrinsic_minmax): Choose type and
	kind of intermediate by looking at all arguments, not the result.

gcc/testsuite/ChangeLog:

	* gfortran.dg/minmax_char_3.f90: New test.
	* gfortran.dg/min_max_kind.f90: New test.
	* gfortran.dg/pr96613.f90: New test.