Revert F16C series (MR 6774)

Revert F16C series (MR 6774)

This reverts commit 4fb2eddfdf9adafde2e6f94de23202ee44123d59.
This reverts commit 7a1deb16f8af4e0ae4ed64511cbfcc606087f0ee.
This reverts commit 2b6a17234376817e75d1f81edf5bd1b28eefb374.
This reverts commit 5af81393e419eaf086e4de2a1d149af78cd1f54d.
This reverts commit 87900afe5bbe90c5f3ad0921b28ae1c889029ada.

A couple of problems were discovered after this series was merged that
cause breakage in different configurations:

   (1) It seems that using -mf16c also enables AVX, leading to SIGILL on
   platforms that do not support AVX.
   (2) Since clang only warns about unknown flags, and as I understand
   it Meson's handling in cc.has_argument() is broken, the F16C code is
   wrongly enabled when clang is used, even for example on ARM, leading
   to a compilation error.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3583
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6969>