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

[via cfe-commits]

JVApen wrote:

Checking the example of https://clang.llvm.org/docs/StandardCPlusPlusModules.html#abi-breaking-style, there is not really and end where to put the include.

It might be advised to put the headers all together after the global module fragment, though restricting the range to that might be to strict. Especially if there are includes after than, it might be advised to group with those.

We also know that the algorithm tries to put the headers as early as possible, so I believe it's safe to not change the max.

If we learn more about modules, we can always add some rule for the max later on.

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