Rework precision setup in genmodes.

Rework precision setup in genmodes.

2022-01-05   Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* gcc/config/rs6000/rs6000-modes.h: Delete.
	* config/rs6000/rs6000-modes.def (rs6000-modes.h): Remove inclusion.
	(IFmode): Rework set up to use FRACTIONAL_FLOAT_MODE_NO_WIDEN.  Use 128
	as the precision.
	(KFmode): Likewise.
	(TFmode): Use FRACTIONAL_FLOAT_MODE, and not
	FRACTIONAL_FLOAT_MODE_NO_WIDEN.  Set the precision to 128.
	* config/rs6000/rs6000.cc (rs6000_option_override_internal): Use 128
	bits as the precision for 128-bit float, instead of special values for
	the 3 different 128-bit FP modes.
	* config/rs6000/rs6000.h (rs6000-modes.h): Remove inclusion.
	* config/rs6000/t-rs6000 (TM_H): Don't add rs6000-modes.h.
	* genmodes.cc (struct mode_data): Add no widen field.
	(blank_mode): Likewise.
	(FRACTIONAL_FLOAT_MODE): Add support for NO_WIDEN capability.
	(FRACTIONAL_FLOAT_MODE_NO_WIDEN): New macro.
	(make_float_mode): Add support for NO_WIDEN capability.
	(emit_mode_wider): Likewise.
	* machmode.def (FRACTIONAL_FLOAT_MODE_NO_WIDEN): Document.