Fix ICE on warning with new interface check.

Fix ICE on warning with new interface check.

In the test case, there was a warning about INTENT where an EXTERNAL
masked an interface in an outer scope, when the location of the
symbol was not set, leading to an ICE.

Two problems, two-part solution: It makes no sense to warn about
INTENT for artificially generated formal argument lists, and the
location should be set.

gcc/fortran/ChangeLog:

	PR fortran/96073
	* frontend-passes.c (check_externals_procedure):  Add locus
	information for new_sym.
	* interface.c (gfc_check_dummy_characteristics): Do not warn
	about INTENT for artificially generated variables.

gcc/testsuite/ChangeLog:

	PR fortran/96073
	* gfortran.dg/interface_48.f90: New test.