Memory limiting does not work on macOS

The limiting of memory via `--max-memory` does not work properly on macOS. For example, if you run
```
$ retdec-fileinfo --max-memory=4096 FILE
```
the analysis (properly) fails on Linux and Windows, but finishes successfully on macOS. The reason is that on macOS, the following piece of code from `src/utils/memory.cpp` compiles, runs, returns 0 (success), but does actually not do anything:
```cpp
struct rlimit rl = {
.rlim_cur = limit, // Soft limit.
.rlim_max = RLIM_INFINITY // Hard limit (ceiling for rlim_cur).
};
auto rc = setrlimit(RLIMIT_AS, &rl);
```
From what I was able to find, `setrlimit()` with `RLIMIT_AS` is broken on macOS and simply does not work.

What is the proper way of programmatically limiting virtual memory on macOS? Feel free to submit a [PR](https://github.com/avast-tl/retdec/pulls) that fixes the implementation of `limitSystemMemoryOnMacOS()` in `src/utils/memory.cpp`.

Start in src/utils/memory.cpp at limitSystemMemoryOnMacOS() and reproduce the issue with retdec-fileinfo --max-memory=4096 FILE on macOS. Compare the macOS behavior with the working Linux and Windows implementations, then verify that the implementation actually limits virtual memory and causes the analysis to fail when the limit is exceeded.

Written by the indexing model from the issue text.