RISC-V: Error if function declared with different interrupt modes.

RISC-V: Error if function declared with different interrupt modes.

	gcc/
	2018-07-06  Kito Cheng  <kito.cheng@gmail.com>
        * config/riscv/riscv.c (enum riscv_privilege_levels): Add UNKNOWN_MODE.
        (riscv_expand_epilogue): Add assertion to check interrupt mode.
        (riscv_set_current_function): Extract getting interrupt type to new
        function.
        (riscv_get_interrupt_type): New function.
        (riscv_merge_decl_attributes): New function, checking interrupt type is
        same.
        (TARGET_MERGE_DECL_ATTRIBUTES): Define.

	gcc/testsuite/
	2018-07-06  Kito Cheng  <kito.cheng@gmail.com>
        * gcc.target/riscv/interrupt-conflict-mode.c: New.

From-SVN: r262607