Use function attributes for SSE 4.2 even when targeting that extension

Use function attributes for SSE 4.2 even when targeting that extension

On Red Hat 9 systems (or similar), the packaged gcc targets x86-64-v2,
but clang does not. This has caused build failures in the wake of
commit e2809e3a1 when building --with-llvm.

The most expedient fix is to use the same function attributes for
the inlined function as we do for the global function.

Reported-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com> (plus members skimmer and bumblebee)
Diagnosed-by: Tom Lane <tgl@sss.pgh.pa.us>
Tested-by: Todd Cook <cookt@blackduck.com>
Discussion: https://postgr.es/m/CANWCAZZSxs3a1YRKehkgk2OHKbrVn+xZ+AWW8Co2R_f70NqqmA@mail.gmail.com