[lld][WebAssembly] Apply relocations to TLS data

This is only needed in the case of dynamic linking and pthreads.
Previously these relocations were simply not being applied.

Verified that this works using a more real world emscripten test:
https://github.com/emscripten-core/emscripten/pull/18641

Differential Revision: https://reviews.llvm.org/D143020