[lld][WebAssembly] Fix for TLS + --relocatable

[lld][WebAssembly] Fix for TLS + --relocatable

When running in `-r/--relocatable` we output relocations but the
new TLS relocations type was missing from `ObjFile::calcNewAddend`
causing this combination of inputs/flags to crash the linker.

Also avoid creating tls variables in relocatable mode.  These variables
are only needed when linking final executables.

Fixes: https://github.com/emscripten-core/emscripten/issues/12934
Fixes: PR48506

Differential Revision: https://reviews.llvm.org/D93554