gcc: xtensa: make register elimination data static

gcc: xtensa: make register elimination data static

Remove ABI reference from the ELIMINABLE_REGS to avoid static data
initialization dependency on xtensa core configuration.

2020-06-15  Max Filippov  <jcmvbkbc@gmail.com>
gcc/
	* config/xtensa/xtensa.c (xtensa_can_eliminate): New function.
	(TARGET_CAN_ELIMINATE): New macro.
	* config/xtensa/xtensa.h
	(XTENSA_WINDOWED_HARD_FRAME_POINTER_REGNUM)
	(XTENSA_CALL0_HARD_FRAME_POINTER_REGNUM): New macros.
	(HARD_FRAME_POINTER_REGNUM): Define using
	XTENSA_*_HARD_FRAME_POINTER_REGNUM.
	(ELIMINABLE_REGS): Replace lines with HARD_FRAME_POINTER_REGNUM
	by lines with XTENSA_WINDOWED_HARD_FRAME_POINTER_REGNUM and
	XTENSA_CALL0_HARD_FRAME_POINTER_REGNUM.