- Clean up build flags for Libreswan. In Libreswan 4.1, these flags are now set automatically based on Ubuntu/Debian versions, and no longer needed for CentOS/RHEL 7 and 8. - Ref: https://github.com/libreswan/libreswan/blob/main/mk/defaults/linux.mk https://github.com/libreswan/libreswan/commit/c01ffcc1