[clang] Reland "[clang][modules-driver] Add support for C++ named modules and import std" (2nd attempt) (PR #194475)

[Naveen Seth Hanig via cfe-commits]

naveen-seth wrote:

> Is there some race-condition going on for the clang/test/Driver/modules-driver-both-modules-types.cpp testcase?
> 
> I've randomly seen
> 
> ```
> clang: ../../clang/lib/DependencyScanning/InProcessModuleCache.cpp:148: virtual std::error_code {anonymous}::InProcessModuleCache::write(llvm::StringRef, llvm::MemoryBufferRef, off_t&, time_t&): Assertion `Entry.Buffer && *Entry.Buffer == Buffer && "Wrote the same PCM with different contents"' failed.
> ```
> 
> in one of our downstream build bots when running that testcase.

Pinging @jansvoboda11 for his expertise on InProcessModuleCache.
I would have time to look into this using tsan after work today otherwise.

https://github.com/llvm/llvm-project/pull/194475