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

[Fangrui Song via llvm-commits]

MaskRay wrote:

I assume that the Fortran compiler that emits `.comm` wants to target WebAssembly. Do you need COMMON symbol's deduplication feature? The compiler can emit a COMDAT section group instead. https://maskray.me/blog/2021-07-25-comdat-and-section-group

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