ci: Use mold for x86-64 and AArch64 builds

mold is a fancy new linker that's really fast.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/6877
Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Eric Engestrom <eric@igalia.com>
Reviewed-by: David Heidelberg <david.heidelberg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17992>

.gitlab-ci/meson/build.sh

@@ -79,7 +79,15 @@ meson _build --native-file=native.file \
       ${EXTRA_OPTION}
 cd _build
 meson configure
-ninja
+if command -V mold &> /dev/null ; then
+    mold --run ninja
+else
+    ninja
+fi
 LC_ALL=C.UTF-8 meson test --num-processes ${FDO_CI_CONCURRENT:-4} --print-errorlogs ${MESON_TEST_ARGS}
-ninja install
+if command -V mold &> /dev/null ; then
+    mold --run ninja install
+else
+    ninja install
+fi
 cd ..