lang/gcc14-devel: Update to 14.0.1.s20240225

Also require to choose a BOOSTRAP option: building GCC with bootstrap
disabled is intended to be possible only when GCC is built with some
pre-installed GCC, however Clang is the default compiler on FreeBSD.

Indeed, bugs have already been encountered when trying to build GCC with
Clang without bootstrap on FreBSD. See for example commit
a4831f49.