[WebAssembly] MC: Fix for data aliases with offsets (getelementptr)

For some reason we hadn't seen such cases in the wild which makes
me think that clang and rustc don't generate these.  In the bug which
reproduces it only occurs with LTO so my guess is that some LTO pass
is creating this alias + gep.

See: https://github.com/emscripten-core/emscripten/issues/8731

Differential Revision: https://reviews.llvm.org/D79462