Introduce vxworks specific crtstuff support

2019-11-06  Jerome Lambourg  <lambourg@adacore.com>
            Olivier Hainque  <hainque@adacore.com>

	libgcc/
	* config/vxcrtstuff.c: New file.
	* config/t-vxcrtstuff: New Makefile fragment.
	* config.host: Append t-vxcrtstuff to the tmake_file list
	on all VxWorks ports using dwarf for table based EH.

	gcc/
	* config/vx-common.h (USE_TM_CLONE_REGISTRY): Remove
	definition, pointless with a VxWorks specific version
	of crtstuff.
	(DWARF2_UNWIND_INFO): Conditionalize on !ARM_UNWIND_INFO.
	* config/vxworks.h (VX_CRTBEGIN_SPEC, VX_CRTEND_SPEC):
	New local macros, controlling the addition of vxworks specific
	crtstuff objects depending on the EH mechanism and kind of
	module being linked.
	(VXWORKS_STARTFILE_SPEC, VXWORKS_ENDFILE_SPEC): Use them.

Co-Authored-By: Olivier Hainque <hainque@adacore.com>

From-SVN: r278248