Fortran: Add error for subroutine passed to a variable dummy [PR106999]

Fortran: Add error for subroutine passed to a variable dummy [PR106999]

2024-04-02  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/106999
	* interface.cc (gfc_compare_interfaces): Add error for a
	subroutine proc pointer passed to a variable formal.
	(compare_parameter): If a procedure pointer is being passed to
	a non-procedure formal arg, and there is an an interface, use
	gfc_compare_interfaces to check and provide a more useful error
	message.

gcc/testsuite/
	PR fortran/106999
	* gfortran.dg/pr106999.f90: New test.

(cherry picked from commit a7aa9455a8b9cb080649a7357b7360f2d99bcbf1)