[clang] [clang-tools-extra] [clangd] [C++20] [Modules] Build Database Support (PR #199384)

[Matthew Asplund via cfe-commits]

mwasplund wrote:

Forgot one other change: Removed GlobalCompilationDatabase from the ModuleFileCache since it was being placed on there and then only used by the parent ModuleBuilder. 

https://github.com/llvm/llvm-project/pull/199384