[llvm] [Runtimes] Merge 'compile_commands.json' files from runtimes build (PR #116303)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

So, on my machine it takes about 0.3 seconds to merge an 8 MB compile commands into a 23 MB one. That'll likely be done in parallel, that time is somewhat similar to some of the worse feature tests in CMake so it might not be too much of an issue.

https://github.com/llvm/llvm-project/pull/116303