RISC-V: Add patterns for vector-scalar multiply-(subtract-)accumulate [PR119100]

RISC-V: Add patterns for vector-scalar multiply-(subtract-)accumulate [PR119100]

This pattern enables the combine pass (or late-combine, depending on the case)
to merge a vec_duplicate into a plus-mult or minus-mult RTL instruction.

Before this patch, we have two instructions, e.g.:
  vfmv.v.f       v6,fa0
  vfmacc.vv      v2,v6,v4

After, we get only one:
  vfmacc.vf      v2,fa0,v4

	PR target/119100

gcc/ChangeLog:

	* config/riscv/autovec-opt.md (*<optab>_vf_<mode>): Handle both add and
	acc FMA variants.
	* config/riscv/vector.md (*pred_mul_<optab><mode>_scalar_undef): New.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/vx_vf/vf-1-f16.c: Add vfmacc and vfmsac.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-1-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-1-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-2-f16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-2-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-2-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-3-f16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-3-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-3-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-4-f16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-4-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf-4-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_mulop.h: Add support for acc
	variants.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_mulop_run.h: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmadd-run-1-f16.c: Define
	TEST_OUT.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmadd-run-1-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmadd-run-1-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmsub-run-1-f16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmsub-run-1-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmsub-run-1-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfnmadd-run-1-f16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfnmadd-run-1-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfnmadd-run-1-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfnmsub-run-1-f16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfnmsub-run-1-f32.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfnmsub-run-1-f64.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmacc-run-1-f16.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmacc-run-1-f32.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmacc-run-1-f64.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmsac-run-1-f16.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmsac-run-1-f32.c: New test.
	* gcc.target/riscv/rvv/autovec/vx_vf/vf_vfmsac-run-1-f64.c: New test.