gcc: xtensa: allow XCHAL_* macros to be non-constant

XCHAL_* macros from the xtensa-config.h are used in a number of places
that require them to be preprocessor constants. Rewrite these places so
that non-constant XCHAL_* definitions could be used there.

2017-06-14  Max Filippov  <jcmvbkbc@gmail.com>
gcc/
	* config/xtensa/xtensa.c (xtensa_option_override): Append
	MASK_CONST16 to target_flags in the absence of TARGET_L32R.
	(hwloop_optimize, hwloop_fail, hwloop_pattern_reg,
	 xtensa_doloop_hooks): Define unconditionally.
	(xtensa_reorg_loops): Only call reorg_loops in the presence of
	TARGET_LOOPS.
	* config/xtensa/xtensa.h (TARGET_L32R): New definition.
	(TARGET_DEFAULT): Remove XCHAL_HAVE_L32R condition and account
	for it in xtensa_option_override.
	(HARD_FRAME_POINTER_IS_FRAME_POINTER,
	 HARD_FRAME_POINTER_IS_ARG_POINTER): New definitions.

From-SVN: r249202