[PATCH v2 1/3] RISC-V: movmem for RISCV with V extension

This patchset permits generation of inlined vectorised code for movmem,
setmem and cmpmem, if and only if the operation size is
at least one and at most eight vector registers' worth of data.

Further vectorisation rapidly becomes debatable due to code size concerns;
however, for these simple cases we do have an unambiguous performance win
without sacrificing too much code size compared to a libc call.

Changes in v2:

* run clang-format over the code in addition to the
  contrib/check_GNU_style.sh that was used for v1

* remove string.h include and refer to __builtin_* memory functions
  in multilib tests

* respect stringop_strategy (don't vectorise if it doesn't include VECTOR)

* use an integer constraint for movmem length parameter

* use TARGET_MAX_LMUL unless riscv-autovec-lmul=dynamic
  to ensure we respect the user's wishes if they request specific lmul

* add new unit tests to check that riscv-autovec-lmul is respected

* PR target/112109 added to changelog for patch 1/3 as requested

Sergei Lewis (3):
  RISC-V: movmem for RISCV with V extension
  RISC-V: setmem for RISCV with V extension
  RISC-V: cmpmem for RISCV with V extension

gcc/ChangeLog

	* config/riscv/riscv.md (movmem<mode>): Use riscv_vector::expand_block_move,
	if and only if we know the entire operation can be performed using one vector
	load followed by one vector store

gcc/testsuite/ChangeLog

	PR target/112109
	* gcc.target/riscv/rvv/base/movmem-1.c: New test