RISC-V: Implement -mmemcpy-strategy= options[PR112537]

RISC-V: Implement -mmemcpy-strategy= options[PR112537]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112537

-mmemcpy-strategy=[auto|libcall|scalar|vector]

auto: Current status, use scalar or vector instructions.
libcall: Always use a library call.
scalar: Only use scalar instructions.
vector: Only use vector instructions.

	PR target/112537

gcc/ChangeLog:

	* config/riscv/riscv-opts.h (enum riscv_stringop_strategy_enum): Strategy enum.
	* config/riscv/riscv-string.cc (riscv_expand_block_move): Disabled based on options.
	(expand_block_move): Ditto.
	* config/riscv/riscv.opt: Add -mmemcpy-strategy=.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/cpymem-strategy-1.c: New test.
	* gcc.target/riscv/rvv/base/cpymem-strategy-2.c: New test.
	* gcc.target/riscv/rvv/base/cpymem-strategy-3.c: New test.
	* gcc.target/riscv/rvv/base/cpymem-strategy-4.c: New test.
	* gcc.target/riscv/rvv/base/cpymem-strategy-5.c: New test.
	* gcc.target/riscv/rvv/base/cpymem-strategy.h: New test.