Merge pull request #35266 from abbradar/cc-bools

cc-wrapper: fix bool handling for empty and zero values

pkgs/build-support/cc-wrapper/utils.sh

@@ -25,7 +25,11 @@ mangleVarBool() {
     for infix in "${role_infixes[@]}"; do
         local inputVar="${var/+/${infix}}"
         if [ -v "$inputVar" ]; then
-            let "${outputVar} |= ${!inputVar}"
+            # "1" in the end makes `let` return success error code when
+            # expression itself evaluates to zero.
+            # We don't use `|| true` because that would silence actual
+            # syntax errors from bad variable values.
+            let "${outputVar} |= ${!inputVar:-0}" "1"
         fi
     done
 }