[RISCV] Add %~ to print w if TARGET_64BIT and use it

[RISCV] Add %~ to print w if TARGET_64BIT and use it

To make things easier and more maintainable, we need to
add support printing out w if TARGET_64BIT so this patch
adds %~ to do that, similar how the x86 backend uses %~
to print out i/f for TARGET_AVX2. We could have chosen any
punctuation symbol but ~ looks the closest to w.

OK? Build and tested for riscv64-linux-gnu and riscv32-linux-gnu with no regressions.

Thanks,
Andrew Pinski

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_print_operand):
	Handle '~'.
	(riscv_print_operand_punct_valid_p): New function
	(TARGET_PRINT_OPERAND_PUNCT_VALID_P): Define.
	* config/riscv/bitmanip.md (<bitmanip_optab>si2/clz_ctz_pcnt):
	Use %~ instead of conditional the pattern on TARGET_64BIT.
	(rotrsi3): Likewise.
	(rotlsi3): Likewise.
	* config/riscv/riscv.md: Add ~ to the list of modifiers.
	(addsi3): Use %~ instead of conditional the pattern on TARGET_64BIT.
	(subsi3): Likewise.
	(negsi2): Likewise.
	(mulsi3): Likewise.
	(optab>si3/any_div): Likewise.
	(*add<mode>hi3): Likewise.
	(<optab>si3/any_shift): Likewise.