What's the point of having all this source code if you can't customize your operating system? FreeBSD not only gives you the source code, it provides ready-to-turn knobs to easily customize your FreeBSD build.
These options can be set in either /etc/make.conf (see Chapter 10) or /etc/src.conf. Settings in src.conf only apply to building the FreeBSD source, while make.conf's settings apply to all source code building. While the full list of src.conf options are documented in src.conf(5), Table 13-2 shows options that I find useful on occasion. We make heavy use of these options in Chapter 20.
The build system checks to see if any of these variables are defined. Setting
WITHOUT_TOOLCHAIN=NO undefines the variable, but using anything ...