[lld][WebAssembly] Allow relocations against non-live global symbols

Just like the in case for function and data symbols this is needed to
support relocations in debug info sections which are allowed contains
relocations against non-live symbols.

The motivating use case is an object file that contains debug info that
references `__stack_pointer` (a local symbol) but does not actually
contain any uses of `__stack_pointer`.

Fixes: https://github.com/emscripten-core/emscripten/issues/14025

Differential Revision: https://reviews.llvm.org/D101399