On Red Hat-derived OSs, /usr/lib/dri contains 32-bit drivers (with
their 64-bit equivalents in /usr/lib64/dri), but on Arch Linux-derived
OSs it contains 64-bit drivers (with their 32-bit equivalents in
/usr/lib32/dri). As a result, we have to run both
i386-linux-gnu-capsule-capture-libs and
x86_64-linux-gnu-capsule-capture-libs against
if-exists:path-match:/usr/lib/dri/*.so, ignoring anything we find that
is of the other word-size.

Signed-off-by: Simon McVittie <smcv@collabora.com>