RISC-V: Add zicond tests

RISC-V: Add zicond tests

These are tests from patch 3/5 of Ziao Zeng's zicond submission.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/zicond-primitiveSemantics_return_0_imm.c: New test.
	* gcc.target/riscv/zicond-primitiveSemantics_return_imm_imm.c: New test.
	* gcc.target/riscv/zicond-primitiveSemantics_return_imm_reg.c: New test.
	* gcc.target/riscv/zicond-primitiveSemantics_return_reg_reg.c: New test.

Co-Authored-By: Jeff Law  <jlaw@ventanamicro.com>