[clang] Insert headers in global module fragment (PR #151624)

[Mythreya Kuricheti via cfe-commits]

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MythreyaK wrote:

Should I combine all into the same test case, or are 3 separate ones okay? 

I just realized the other tests seem to combine multiple checks into one gtest test. 

https://github.com/llvm/llvm-project/pull/151624