Saving bytecode objects generates "corrupt .drectve at end of def file" warning on MINGW64

[rdw-software]

When building the runtime using the ninja build system (currently WIP), saving bytecode objects generates the following warning:

Warning: corrupt .drectve at end of def file

Going by the LuaJIT issue, this isn't a problem but rather necessary to compile with MSVC (which I don't care about).

Since it's somewhat annoying and may be confusing it should likely be fixed for MINGW64-based builds. Maybe the objects' exported directive can be patched using standard Unix tools (via CLI, after building the objects)? If not, could consider patching the Lua module responsible for it (in the build directory's jit folder).