RISC-V: Fix interrupt support for -g.

RISC-V: Fix interrupt support for -g.

	gcc/
	* config/riscv/riscv.c (riscv_expand_epilogue): Use emit_jump_insn
	instead of emit_insn for interrupt returns.
	* config/riscv/riscv.md (riscv_met): Add (return) to rtl.
	(riscv_sret, riscv_uret): Likewise.

	gcc/testsuite/
	* gcc.target/riscv/interrupt-debug.c: New.

From-SVN: r262327