Use movi + element move instead of a load for _mm_set_ss
Use movi + element move instead of a load for _mm_set_ss

Some compilers will not optimise vld1q_f32({a, 0, 0, 0}) to a movi +
mov, so explicitly implement _mm_set_ss as such.

Example codegen for _mm_set_ss(a) with GCC 11.2.0 (-O3):

Prior to commit:
    sub     sp, sp, 0x10
    stp     xzr, xzr, [sp]
    str     s0, [sp]
    ldr     q0, [sp]
    add     sp, sp, 0x10

After commit:
    movi    v1.4s, 0x0
    mov     v1.s[0], v0.s[0]
    mov     v0.16b, v1.16b

DLTcollab/sse2neon,DLTcollab/sse2neon,DLTcollab/sse2neon