[WebAssembly][lld] Fix for static linking of PIC code

When statically linking PIC code we create an internalized __memory_base
so that memory-base-relative relocation work correctly.  The value of
this global should be zero, and not the globalBase since the globalBase
offset is already taken into account by getVirtualAddress.

Fixes: https://github.com/emscripten-core/emscripten/issues/9013

Differential Revision: https://reviews.llvm.org/D69600