ci: pass -Werror using CFLAGS

Judging by https://github.com/systemd/systemd/issues/16224, it seems
`--werror` doesn't work with `-Db_lto=true`

diff --git a/.github/workflows/ubuntu-build-check.sh b/.github/workflows/ubuntu-build-check.sh
index fb7c71ecb89a182f8faa0ea1c4e23ddac05cbf1e..75fc36fffb10fcf1b5664e509d294a4bfa3bdcf3 100755 (executable)
--- a/.github/workflows/ubuntu-build-check.sh
+++ b/.github/workflows/ubuntu-build-check.sh
@@ -102,7 +102,7 @@ for args in "${ARGS[@]}"; do
     SECONDS=0
 
     info "Checking build with $args"
-    if ! AR="$AR" CC="$CC" CXX="$CXX" meson -Dtests=unsafe -Dslow-tests=true --werror $args build; then
+    if ! AR="$AR" CC="$CC" CXX="$CXX" CFLAGS="-Werror" CXXFLAGS="-Werror" meson -Dtests=unsafe -Dslow-tests=true --werror $args build; then
         fatal "meson failed with $args"
     fi