These are emitted by GCC when -Wundef is passed.
The _PSX symbol looks to be intended to switch the codebase between
building the PSX and PC version of the game due to differences in the
data structures. The _PSX_ON_PC likely allows building a version of
the engine which will run on PC, but use the PSX game data.
These should be refactored to allow the codebase to use either PC or
PSX game data at runtime in future, but for now, these are hardcoded
to the PC game data version for build stability.
