[clang] [clang/DependencyScanning/ModuleDepCollector] Refactor part of `makeCommonInvocationForModuleBuild` into its own function, NFC (PR #88447)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 approved this pull request.

LGTM. I assume you'll call `resetBenignCodeGenOptions()` from `ModuleDepCollector::applyDiscoveredDependencies()` in a follow-up, non-NFC patch, right? (So that it applies to the primary invocation, i.e. the actual PCH.) Maybe leaving a FIXME behind would be nice, just to make the intent clear.

https://github.com/llvm/llvm-project/pull/88447