For those who are interested in which sources aren't included:

https://www.nordier.com/v7x86/files/RELNOTES

"The following limitations apply to the distribution:

- The source to the C compiler is not part of the distribution. This is currently built separately as a component of a modified version of the Amsterdam Compiler Kit (ACK).

- The source for boot (the second stage bootstrap) is not part of the distribution. This is currently built separately using a 16-bit version of pcc."

The compilers mentioned:

https://en.wikipedia.org/wiki/Amsterdam_Compiler_Kit

https://en.wikipedia.org/wiki/Portable_C_Compiler