GitLab

Move functions that read process data into LinuxProcess.c
and change flow from a monolithic `ProcessList_scan ->
ProcessList_goThroughEntries` into the following:

```
ProcessList_scan -> (Linux)ProcessList_goThroughEntries ->
ProcessList_scanProcess -> (Linux)Process_update
```

This will allow hooking plugins into the scanning
process.

Other platforms need to be similarly reworked.

Calls marked with xSnprintf shouldn't fail.
Abort program cleanly if any of them does.

__attribute__((nonnull)) will help catching "calling with NULL" mistake on
compile time.

I also convert xStrdup into a macro, that will do assert() inline when the
code is *not* built with -DNDEBUG . For release builds (with -DNDEBUG),
preprocessor trick will ensure that generated code remains the same.