Does C++ extractor support to process code with unity build?

**Description of the issue**
Does C++ extractor support to process code with unity build? I recently tried to use codeql in a c++ project with unity build, but many file extractions failed.
unity build: https://en.wikipedia.org/wiki/Unity_build

Start by reproducing the reported extraction failures with a C++ unity build and inspect the extractor behavior. The issue does not name files, tests, or an entry point, so determine the relevant extractor area and define whether successful processing or a documented limitation is the expected outcome.

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