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

[Fangrui Song via llvm-commits]

MaskRay wrote:

The COMMON symbol in COFF, Mach-O, and ELF formats shares a key property: the linker allocates sufficient space to accommodate the largest size required. In contrast, a weak symbol fallback does not meet this requirement. This distinction raises concerns about introducing another method to generate weak symbols, potentially causing confusion.
To address this, you should modify LLVM API users to avoid relying on the common symbol and update any software intended for WebAssembly to disable the -fcommon flag.

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