build-gnu.sh: Do not build GNU coreutils for faster CI

Author: oech3

util/build-gnu.sh

@@ -138,7 +138,7 @@ else
     sed -i 's| tr | /usr/bin/tr |' tests/init.sh
     # Use a better diff
     sed -i 's|diff -c|diff -u|g' tests/Coreutils.pm
-    "${MAKE}" -j "$("${NPROC}")"
+    CFLAGS="${CFLAGS} -pipe -std=c23" "${MAKE}" -j "$("${NPROC}")" src/getlimits # needed for tests
 
     # Handle generated factor tests
     t_first=00