ci: build with -Werror on Fedora

Prompted by: systemd#18400 (comment)

.packit.yml

@@ -22,8 +22,18 @@ actions:
     # - Patch0000-0499: backported patches from upstream
     # - Patch0500-9999: downstream-only patches
     - "sed -ri '/^Patch0[0-4][0-9]{2}+\\:.+\\.patch/d' .packit_rpm/systemd.spec"
-    # Build the RPMs with -Werror to catch possible compiler warnings
-    - "sed -i 's/^%meson /%meson --werror /' .packit_rpm/systemd.spec"
+    # Build the RPMs with -Werror to catch possible compiler warnings. Since
+    # --werror in meson doesn't seem to work with -Db_lto=true [0], let's use
+    # -Dc_args= and -Dcpp_args= instead.
+    #
+    # Exceptions:
+    #   - use -Wno-deprecated-declarations to get around mallinfo() use in
+    #     basic/selinux-util.c
+    #   - don't use -Werror on x86 architectures, otherwise all function checks
+    #     will fail (with error: cast from pointer to integer of different size)
+    #
+    # [0] https://github.com/mesonbuild/meson/issues/7360
+    - 'sed -i "/^CONFIGURE_OPTS=(/a%ifnarch i386 i686\n-Dc_args=\"-Werror -Wno-deprecated-declarations\" -Dcpp_args=\"-Werror -Wno-deprecated-declarations\"\n%endif" .packit_rpm/systemd.spec'
 
 jobs:
 - job: copr_build