RISCV test infrastructure for d / v / zfh extensions

RISCV test infrastructure for d / v / zfh extensions

gcc/testsuite/
	* lib/target-supports.exp (check_effective_target_rv_float_abi_soft):
	New proc.
	(check_effective_target_riscv_d): Likewise.
	(check_effective_target_riscv_v): Likewise.
	(check_effective_target_riscv_zfh): Likewise.
	(check_effective_target_riscv_v_ok): likewise.
	(check_effective_target_riscv_zfh_ok): Likewise.
	(riscv_get_arch, add_options_for_riscv_v): Likewise.
	(add_options_for_riscv_zfh): Likewise.
	(add_options_for_riscv_d): Likewise.