Improving the FreeBSD Build

The FreeBSD build has mostly seen small incremental improvements over the years and a lot of bitrot. Not many people are active today that understand all of the pieces involved in the build. While some recent work is moving towards a drastically new build, much of the work is also benefiting the historical buildworld which most people are used to and is likely to prevail. The ability to build a subset of the tree is a large goal of this effort since it is a big productivity loss for developers. Improving the speed of buildworld is being done while working towards the new build goals.

Recent improvements to be covered: * External toolchains. * More parallelization of buildworld and bsd.subdir.mk. * FASTDEPEND: Generating dependencies at compile time with GCC 3.0 flags rather than pre-processing files before compiling them and then pre-processing them again. This brings a 16% buildworld improvement and 35% to buildkernel. * Removing the need for 'make depend'. * CCACHEBUILD: Built-in ccache support. This brings up to 65% incremental build time improvement when combined with FASTDEPEND. * LIBADD and its improvements. * DIRDEPSBUILD (Presented by Simon Gerraty in 2014 as "meta mode") improvements, which bring reliable sub-directory builds. * Incremental build fixes for stealth dependencies. * WITHSYSTEMCOMPILER: Skipping building clang sometimes * WITHMETAMODE: reliable incremental buildworld

Planned work to be covered: * Adding more build-time assertions to ensure the framework is used properly, such as was done with great success in Ports. * Library over/under-link testing. * Building clang once for make universe * Reducing duplicated dependency logic and redundant phases in buildworld. * Foreign building, such as from OSX or Linux. * Ports cross-building without QEMU, as it is not always feasible to use it.