PR 122245: -fc-prototypes when procedure defined via INTERFACE

This simple patch emits correct prototypes when a procedure is
defined via an interface by simply checking the presence
of an interface and using its formal arglist.

gcc/fortran/ChangeLog:

	PR fortran/122245
	* dump-parse-tree.cc (write_formal_arglist): Take the formal
	arglist from the symbol's interface if it is present.