Clangd appears to only work after being run a second time

[robmck1995]

The C references test that is consistently failing does not show up when running locally (after the first run).

This is because locally, clangd creates the compile_commands.json and the cache files in the local checkout on the first run, and then after that the test passes.

In CI this consistently fails as the checkout does not have the cache files. We should resolve this issue.

[maks-ivanov]

I think this might be a speed thing - I.e. on the first run, if the test execution was delayed until indexing is complete it would pass. This problem is potentially more severe on CI machines because they are weaker than our local setups. Should be easily verifiable with a sleep