[clang] [llvm] [clang][WebAssembly] support custom module name of import globals (PR #200722)

[Changqing Jing via cfe-commits]

Changqing-JING wrote:

@dschuff
Thank you very much for your reply.

Actually I tried similar thing with #201966 locally. The reason why I didn't push this version is, I want to make this PR be limited within LLVM backend. I have some concern that if I change the [‎clang/include/clang/Basic/Attr.td‎](https://github.com/llvm/llvm-project/pull/200722#diff-ae2ec9524bdbeea1f06917607482634dd89af5bcbb929805032463e5dafe79e7), it is a wide change in clang and the PR may not be accepted.

But I also agree that if #201966 can be merged, it provides a much better user experience than current PR.

So since you have already created this PR, I would recommend to try #201966 first. If it's merged, I will close this one. Otherwise we can use this one as a backup plan. 

https://github.com/llvm/llvm-project/pull/200722