RISC-V: Fix incorrect combine of extended scalar pattern

RISC-V: Fix incorrect combine of extended scalar pattern

Background:
RVV ISA vx instructions for example vadd.vx,
When EEW = 64 and RV32. We can't directly use vadd.vx.
Instead, we need to use:

sw
sw
vlse
vadd.vv

However, we have some special situation that we still can directly use
vadd.vx directly for EEW=64 && RV32.

that is, when scalar is a known CONST_INT value that doesn't overflow 32-bit value.
So, we have a dedicated pattern for such situation:

...
(sign_extend:<VEL> (match_operand:<VSUBEL> 3 "register_operand"          " r,  r,  r,  r")).
...

We first force_reg such CONST_INT (within 32bit value) into a SImode reg.
Then use such special patterns.
Those pattern with this operand match should only value on! TARGET_64BIT.

The PR112801 combine into such patterns on RV64 incorrectly (Those patterns should be only value on RV32).

This is the bug:

        andi    a2,a2,2
        vsetivli        zero,2,e64,m1,ta,ma
        sext.w  a3,a4
        vmv.v.x v1,a2
        vslide1down.vx  v1,v1,a4    -> it should be a3 instead of a4.

Such incorrect codegen is caused by
...
                (sign_extend:DI (subreg:SI (reg:DI 135 [ f.0_3 ]) 0))
            ] UNSPEC_VSLIDE1DOWN)) 16935 {*pred_slide1downv2di_extended}
...

Incorretly combine into the patterns should not be valid on RV64 system.

So add !TARGET_64BIT to all same type patterns which can fix such issue as well as robostify the vector.md.

	PR target/112801

gcc/ChangeLog:

	* config/riscv/vector.md: Add !TARGET_64BIT.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/pr112801.c: New test.