Fix ICE on invalid, PR94090.

Fix ICE on invalid, PR94090.

The attached patch fixes an ICE on invalid: When the return type of
a function was misdeclared with a wrong rank, we issued a warning,
but not an error (unless with -pedantic); later on, an ICE ensued.

Nothing good can come from wrongly declaring a function type
(considering the ABI), so I changed that into a hard error.

2020-04-17  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/94090
	* gfortran.dg (gfc_compare_interfaces): Add
	optional argument bad_result_characteristics.
	* interface.c (gfc_check_result_characteristics): Fix
	whitespace.
	(gfc_compare_interfaces): Handle new argument; return
	true if function return values are wrong.
	* resolve.c (resolve_global_procedure): Hard error if
	the return value of a function is wrong.

2020-04-17  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/94090
	* gfortran.dg/interface_46.f90: New test.