[llvm] Partial support for common linkage for WebAssembly (PR #151478)

[Derek Schuff via llvm-commits]

dschuff wrote:

There is also still plenty of C code out there that depends on `-fcommon` to compile. including a surprisingly large chunk of the LLVM [testsuite](https://github.com/search?q=repo%3Allvm%2Fllvm-test-suite%20fcommon&type=code) that we just can't easily compile to wasm today.

https://github.com/llvm/llvm-project/pull/151478