RISC-V: Add support for 'XVentanaCondOps' reusing 'Zicond' support

RISC-V: Add support for 'XVentanaCondOps' reusing 'Zicond' support

'XVentanaCondOps' is a vendor extension from Ventana Micro Systems
containing two instructions for conditional move and will be supported on
their Veyron V1 CPU.

And most notably (for historical reasons), 'XVentanaCondOps' and the
standard 'Zicond' extension are functionally equivalent (only encodings and
instruction names are different).

*   czero.eqz == vt.maskc
*   czero.nez == vt.maskcn

This commit adds support for the 'XVentanaCondOps' extension by extending
'Zicond' extension support.  With this, we can now reuse the optimization
using the 'Zicond' extension for the 'XVentanaCondOps' extension.

The specification for the 'XVentanaCondOps' extension is based on:
<https://github.com/ventanamicro/ventana-custom-extensions/releases/download/v1.0.1/ventana-custom-extensions-v1.0.1.pdf>

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc (riscv_ext_flag_table):
	Parse 'XVentanaCondOps' extension.
	* config/riscv/riscv-opts.h (MASK_XVENTANACONDOPS): New.
	(TARGET_XVENTANACONDOPS): Ditto.
	(TARGET_ZICOND_LIKE): New to represent targets with conditional
	moves like 'Zicond'.  It includes RV64 + 'XVentanaCondOps'.
	* config/riscv/riscv.cc (riscv_rtx_costs): Replace TARGET_ZICOND
	with TARGET_ZICOND_LIKE.
	(riscv_expand_conditional_move): Ditto.
	* config/riscv/riscv.md (mov<mode>cc): Replace TARGET_ZICOND with
	TARGET_ZICOND_LIKE.
	* config/riscv/riscv.opt: Add new riscv_xventana_subext.
	* config/riscv/zicond.md: Modify description.
	(eqz_ventana): New to match corresponding czero instructions.
	(nez_ventana): Ditto.
	(*czero.<eqz>.<GPR><X>): Emit a 'XVentanaCondOps' instruction if
	'Zicond' is not available but 'XVentanaCondOps' + RV64 is.
	(*czero.<eqz>.<GPR><X>): Ditto.
	(*czero.eqz.<GPR><X>.opt1): Ditto.
	(*czero.nez.<GPR><X>.opt2): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/xventanacondops-primitiveSemantics.c: New test,
	* gcc.target/riscv/xventanacondops-primitiveSemantics-rv32.c: New
	test to make sure that XVentanaCondOps instructions are disabled
	on RV32.
	* gcc.target/riscv/xventanacondops-xor-01.c: New test,