devel/cmake-core: Use fat LTO instead of thin LTO

As we hardcode thin LTO to one thread [1] without any resolve for more
than a year use fat which performs better

1: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=281765

PR: 292178
Approved by: timeout (no objections for 3+ weeks)
Exp-run by: antoine