RISC-V: Bugfix ICE non-vector in TARGET_FUNCTION_VALUE_REGNO_P

RISC-V: Bugfix ICE non-vector in TARGET_FUNCTION_VALUE_REGNO_P

This patch would like to fix one ICE when vector is not enabled
in hook TARGET_FUNCTION_VALUE_REGNO_P implementation.  The vector
regno is available if and only if the TARGET_VECTOR is true.  The
previous implement missed this condition and then result in ICE
when rv64gc build option without vector.

The below test suite is passed for this patch.

* The rv64gcv fully regression tests.
* The rv64gc fully regression tests.

	PR target/114639

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_function_value_regno_p): Add
	TARGET_VECTOR predicate for V_RETURN regno.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/pr114639-1.c: New test.
	* gcc.target/riscv/pr114639-2.c: New test.
	* gcc.target/riscv/pr114639-3.c: New test.
	* gcc.target/riscv/pr114639-4.c: New test.

Signed-off-by: Pan Li <pan2.li@intel.com>