[RDY] Remove project-specific integer types: long_u. (2)

This is part of a series of PR's aimed at removing long_u from the codebase.
This PR deals with the following instances of long_u:

- Those within *eval* module.
- Those within *memfile* module.

It continues the work in #656, #757 towards fulfilling #459.
Hey, I just spotted these lines in build/CMakeCache.txt:
```
//CHECK_TYPE_SIZE: sizeof(off_t)
SIZEOF_OFF_T:INTERNAL=8
```
So, it seems cmake is checking `off_t` size when building. Wouldn't it be possible to generate OFF_T_MAX/MIN constants there? Maybe it's even doing it, but we just didn't know. Anyone who groks cmake?