Static analysis for definition of DO index variables in contained procedures.

Static analysis for definition of DO index variables in contained procedures.

When encountering a procedure call in a DO loop, this patch checks if
the call is to a contained procedure, and if it is, check for
changes in the index variable.

gcc/fortran/ChangeLog:

	PR fortran/96469
	* frontend-passes.c (doloop_contained_function_call): New
	function.
	(doloop_contained_procedure_code): New function.
	(CHECK_INQ): Macro for inquire checks.
	(doloop_code): Invoke doloop_contained_procedure_code and
	doloop_contained_function_call if appropriate.
	(do_intent): Likewise.

gcc/testsuite/ChangeLog:

	PR fortran/96469
	* gfortran.dg/do_check_4.f90: Hide change in index variable
	from compile-time analysis.
	* gfortran.dg/do_check_13.f90: New test.