RISC-V: Error early with V and no M extension.

RISC-V: Error early with V and no M extension.

For calculating the value of a poly_int at runtime we use a
multiplication instruction that requires the M extension.
Instead of just asserting and ICEing this patch emits an early
error at option-parsing time.

gcc/ChangeLog:

	PR target/116036

	* config/riscv/riscv.cc (riscv_override_options_internal): Error
	with TARGET_VECTOR && !TARGET_MUL.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/arch-31.c: Add m to arch string and expect it.
	* gcc.target/riscv/arch-32.c: Ditto.
	* gcc.target/riscv/arch-37.c: Ditto.
	* gcc.target/riscv/arch-38.c: Ditto.
	* gcc.target/riscv/predef-14.c: Ditto.
	* gcc.target/riscv/predef-15.c: Ditto.
	* gcc.target/riscv/predef-16.c: Ditto.
	* gcc.target/riscv/predef-26.c: Ditto.
	* gcc.target/riscv/predef-27.c: Ditto.
	* gcc.target/riscv/predef-32.c: Ditto.
	* gcc.target/riscv/predef-33.c: Ditto.
	* gcc.target/riscv/predef-36.c: Ditto.
	* gcc.target/riscv/predef-37.c: Ditto.
	* gcc.target/riscv/rvv/autovec/pr111486.c: Add m to arch string.
	* gcc.target/riscv/compare-debug-1.c: Ditto.
	* gcc.target/riscv/compare-debug-2.c: Ditto.
	* gcc.target/riscv/rvv/base/pr116036.c: New test.