Bind(c): Improve error checking in CFI_* functions

Bind(c): Improve error checking in CFI_* functions

This patch adds additional run-time checking for invalid arguments to
CFI_establish and CFI_setpointer.  It also changes existing messages
throughout the CFI_* functions to use PRIiPTR to format CFI_index_t
values instead of casting them to int and using %d (which may not work
on targets where int is a smaller type), simplifies wording of some
messages, and fixes issues with capitalization, typos, and the like.
Additionally some coding standards problems such as >80 character lines
are addressed.

2021-07-24  Sandra Loosemore  <sandra@codesourcery.com>

	PR libfortran/101317

libgfortran/
	* runtime/ISO_Fortran_binding.c: Include <inttypes.h>.
	(CFI_address): Tidy error messages and comments.
	(CFI_allocate): Likewise.
	(CFI_deallocate): Likewise.
	(CFI_establish): Likewise.  Add new checks for validity of
	elem_len when it's used, plus type argument and extents.
	(CFI_is_contiguous): Tidy error messages and comments.
	(CFI_section): Likewise.  Refactor some repetitive code to
	make it more understandable.
	(CFI_select_part): Likewise.
	(CFI_setpointer): Likewise.  Check that source is not an
	unallocated allocatable array or an assumed-size array.

gcc/testsuite/
	* gfortran.dg/ISO_Fortran_binding_17.f90: Fix typo in error
	message patterns.