tree.h (categorize_ctor_elements): Adjust prototype and add descriptive comment...

	* tree.h (categorize_ctor_elements): Adjust prototype and add
	descriptive comment, both in accordance with the interface change
	described below.
	* varasm.c (constructor_static_from_elts_p): New function.
	Whether a constructor node is a valid static constant initializer
	if all its elements are.
	(initializer_constant_valid_p) <CONSTRUCTOR value>: Use it.
	* output.h: Declare it.	
	* expr.c (categorize_ctor_elements_1): Return whether the constructor
	is a valid constant initializer instead of computing the number of
	non-constant elements.  Use constructor_static_from_elts_p for this
	purpose.  Replace the head comment with an indication that this is a
	helper for categorize_ctor_elements.
	(categorize_ctor_elements): Same interface change as for the _1
	helper.  Former head comment from this helper moved here, adjusted to
	account for the interface changes.
	(mostly_zeros_p): Adjust call to categorize_ctor_elements.
	(all_zeros_p): Likewise.	
	* gimplify.c (gimplify_init_constructor): Decide whether we can make
	static versions of the constructor from the categorize_ctor_elements
	return value instead of the formerly computed number of non-constant
	elements.

	* gnat.dg/outer_agg_bitfield_constructor.adb: New test.
	* gnat.dg/nested_agg_bitfield_constructor.adb: New test.

From-SVN: r115553