The Borland compilers were single-pass compilers; they did not go through an AST, but generated machine code directly from parser input. Also, the original Turbo Pascal compiler was written in assembly language. (Not sure about the later compiler versions used by BP and Delphi.)

Also, the language was quite simple. With large, complex programs, the most time-consuming stage was in the linking of the final binary.

If you want a similarly fast compiler today, look at Go.