This patch adds support to wasm-ld for linking multiple table references together, in a manner similar to wasm globals. The indirect function table is synthesized as needed.
To manage the transitional period in which the compiler doesn't yet produce TABLE_NUMBER relocations and doesn't residualize table symbols, the linker will detect object files which have table imports or definitions, but no table symbols. In that case it will synthesize symbols for the defined and imported tables.
As a change, relocatable objects are now written with table symbols, which can cause symbol renumbering in some of the tests. If no object file requires an indirect function table, none will be written to the file. Note that for legacy ObjFile inputs, this test is conservative: as we don't have relocs for each use of the indirecy function table, we just assume that any incoming indirect function table should be propagated to the output.