[Ada] Warning for out-of-order record representation clauses

[Ada] Warning for out-of-order record representation clauses

The compiler can now warn for out-of-order record representation
clauses. A warning is given if the order of component declarations,
component clauses, and bit-level layout do not all agree.  The warning
is disabled by default, and may be enabled by the -gnatw_r switch.

2019-08-20  Bob Duff  <duff@adacore.com>

gcc/ada/

	* sem_ch13.adb (Component_Order_Check): New procedure to check
	for out-of-order clauses.
	* warnsw.ads, warnsw.adb: New -gnatw_r switch.
	* doc/gnat_ugn/building_executable_programs_with_gnat.rst:
	Document new switch.
	* gnat_ugn.texi: Regenerate.

From-SVN: r274723