But I advise no one to use it for anything else but compiling Linux. This version supports only a hacked minix object file format, and has a few bugs in 32-bit mode, so you better keep it only for compiling Linux. The most recent versions are published together with the FreeBSD distribution. But your mirror may vary, and the version may evolve. The docs are what is included in the bcc package.
Man pages are also available somewhere on the FreeBSD site.
As an example of its limitations, you can't declare objects so that destructors are automatically called at the end of the declaring block, you can't co-declared data and the code to process it, etc. CPP came with your C compiler. 3.2.2 M4 M4 gives you the full power of macroprocessing, with a Turing equivalent language, recursion, regular expressions, etc. You can do with it everything that CPP cannot. This is NOT worse than CPP that does not allow quoting and recursion anyway.