[clang] [clang][modules] Introduce a flag to keep redundant module lookups on relocation checks (PR #219107)

[Cyndy Ishida via cfe-commits]

https://github.com/cyndyishida commented:

> How redundant are the relocation checks now? 

When the flag is used, its no more redundant than before https://github.com/llvm/llvm-project/commit/cf8597bd3b87aeed6696454f22311e86ed70138f. 

I think that turns out to be once per dependency on the module deserialized from an PCM. IOW whenever `ReadControlBlock` is called to read `MODULE_DIRECTORY`. 

https://github.com/llvm/llvm-project/pull/219107