[clang-tools-extra] [clangd] [Modules] Fixes to correctly handle module dependencies (PR #142090)

[via cfe-commits]

fleeting-xx wrote:

Thank you @ChuanqiXu9 for the review.

Looks like this is causing failures on [arm64 windows builds](https://lab.llvm.org/buildbot/#/builders/161). Not quite sure why. Relevant log contains:
```
# | I[14:07:36.383] Built preamble of size 842464 for file C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\build\tools\clang\tools\extra\clangd\test\Output\modules.test.tmp\Use.cpp version 1 in 0.02 seconds
# | E[14:07:36.414] Failed to build module A; due to Don't get the module unit for module A
```

Going to revert this. I'll see if I can load up a Microsoft Surface I have access to with development tools and investigate. Until I can do so I'll go ahead and revert the change.

https://github.com/llvm/llvm-project/pull/142090