DWARF: create a macro for max dimensions for array descr. lang. hook

DWARF: create a macro for max dimensions for array descr. lang. hook

The array descriptor language hook can hold the description of a limited
number of array dimensions.  This macro will ease preventing overflow in
front-ends.

gcc/ada/ChangeLog:

	* gcc-interface/misc.c (gnat_get_array_descr_info): When the
	array has more dimensions than the language hook can handle,
	fall back to a nested arrays description.  Handle context-less
	array types.

gcc/ChangeLog:

	* dwarf2out.h (DWARF2OUT_ARRAY_DESCR_INFO_MAX_DIMEN): New macro.
	(struct array_descr_info): Use it for the dimensions array's
	size.
	* dwarf2out.c (gen_type_die_with_usage): Check that the array
	descr. language hook does not return an array with more
	dimensions that it should.

From-SVN: r231766