Cross-compilers.
For example, the Burroughs Large System (B6700 etc, which has evolved to Clearpath), was always written in Algol. There was never an assembler for it. A compiler which emitted B6700 code was implemented on a B5000 (different architecture, different instructions), and the output of that compiler was used to boot the B6700. And of course, the compiler was written in Algol, so once the B6700 was running, subsequent compilation could be done on the new system.
Looking at the source code for the MCP, and the patch history of it, there were in fact some lines which dated from the very first iteration.
Biting the hand that feeds IT
