[Nit] fileio patterned incorrectly in Platforms/General

The header `//ENIGMAsystem/SHELL/Platforms/General/fileio.h` includes a helper header, `file_t.h`, which varies between SDL and non-SDL systems. Non-SDL systems should instead alias `FILE` to `FILE_t` themselves, then include the General header (and similarly, SDL should alias it to `SDL_RWops`). This way, we don't have random platform-specific patterns in General. General is meant for general headers.

As a clarifying point, this approach requires an additional search directory to be added, which is handled in the Makefile, but this breaks JDI due to #2419.

The workaround, which I will implement in the meantime, hard-codes this search directory in Clang-JDI.