RISC-V: Disallow regrenme if the TO register never used before for interrupt functions

RISC-V: Disallow regrenme if the TO register never used before for interrupt functions

gcc/ChangeLog

	PR target/93304
	* config/riscv/riscv-protos.h (riscv_hard_regno_rename_ok): New.
	* config/riscv/riscv.c (riscv_hard_regno_rename_ok): New.
	* config/riscv/riscv.h (HARD_REGNO_RENAME_OK): Defined.

gcc/testsuite/ChangeLog

	PR target/93304
	* gcc.target/riscv/pr93304.c: New test.