This issue tracks a very ambitions goal of Devilution, the production of a byte-identical executable to the 1.09b original. To achieve this goal, the exact same compiler has to be used as was used to produce the original executable.

For diablo.exe version 1.09b, this corresponds to Visual C++ 5.10, and for the debug release diablo.exe version 1.00 (1996-12-21) this corresponds to Visual C++ 4.20 compiled in debug mode; as based on PEiD output.

Edit: reference discussion: https://github.com/galaxyhaxz/devilution/pull/10#issuecomment-396211436