database analyze not honoring the memory limits.

I am running the full cpp-lgmt query suite against a big codebase, and specified the memory limit to be 30GB, and 30 jobs, and I think it might be exceeding that limit.

According to HTOP, it is now using 70G of ram (still running and growing), and the number of threads is around 80.

This is the command I invoked:

```shellsession
mvanotti@markov:~/codeql-home$ ./codeql/codeql database analyze fuchsia-ql ql/cpp/ql/src/codeql-suites/cpp-lgtm-full.qls --format=sarif-latest --output=cpp-lgtm.sarif -j 30 -M 30240 --no-rerun
```

Start by reproducing the `codeql database analyze` command from the issue with `-j 30` and `-M 30240`, while monitoring memory use and thread count. The fix is complete when the analysis honors both limits during the reported C++ LGTM suite run.

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