RISC-V: Define __riscv_v_intrinsic [PR109312]

RISC-V: Define __riscv_v_intrinsic [PR109312]

RVV intrinsic has defined a macro to identity the version of RVV
intrinsic spec, we missed that before, thanksful we are catch this
before release.

gcc/ChangeLog:

	PR target/109312
	* config/riscv/riscv-c.cc (riscv_ext_version_value): New.
	(riscv_cpu_cpp_builtins): Define __riscv_v_intrinsic and
	minor refactor.

gcc/testsuite/ChangeLog:

	PR target/109312
	* gcc.target/riscv/predef-__riscv_v_intrinsic.c: New test.