[clang] [clang][MBD] set up module build daemon infrastructure (PR #67562)

[Michael Spencer via cfe-commits]

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+// Check that clang invocation can spawn and handshake with module build daemon
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Bigcheese wrote:

This test should also check that clang can connect to an existing MBD without spawning a new one.

https://github.com/llvm/llvm-project/pull/67562