[Bug target/119626] On ARM, use the bfcvt instruction to cast to __bf16 when target supports it

[mcccs at gmx dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119626

--- Comment #3 from mcccs at gmx dot com ---
Sorry for so many pings, the final code is:

void convert1(int * __restrict a, __bf16 * __restrict x) {
    x[0] = (__bf16)a[0];
    x[1] = (__bf16)a[1];
    x[2] = (__bf16)a[2];
    x[3] = (__bf16)a[3];
}

void convert2(float * __restrict a, __bf16 * __restrict x) {
    x[0] = (__bf16)a[0];
    x[1] = (__bf16)a[1];
    x[2] = (__bf16)a[2];
    x[3] = (__bf16)a[3];
}