ci: Enable -Werror in clang jobs

They're not warning-clean yet, but we can enable -Werror in general and
just allow the existing types of warnings as exceptions with
-Wno-error=[...]. This way, new warnings of all other types will be
prevented from entering the code base.

Once all warnings of a certain type have been eliminated in a job, the
exception for that type can be dropped from that job. This provides a
realistic path to a fully warning-clean CI build in the future.

v2:
* Use echo -n (Juan A. Suarez)

Reviewed-by: Eric Anholt <eric@anholt.net> # v1
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10220>

.gitlab-ci/meson/build.sh

@@ -64,6 +64,8 @@ meson _build --native-file=native.file \
       -D libdir=lib \
       -D buildtype=${BUILDTYPE:-debug} \
       -D build-tests=true \
+      -D c_args="$(echo -n $C_ARGS)" \
+      -D cpp_args="$(echo -n $CPP_ARGS)" \
       -D libunwind=${UNWIND} \
       ${DRI_LOADERS} \
       -D dri-drivers=${DRI_DRIVERS:-[]} \