[WebAssembly] New-style command support This adds support for new-style command support. In this mode, all exports are considered command entrypoints, and the linker inserts calls to `__wasm_call_ctors` and `__wasm_call_dtors` for all such entrypoints. This enables support for: - Command entrypoints taking arguments other than strings and return values other than `int`. - Multicall executables without requiring on the use of string-based command-line arguments. This new behavior is disabled when the input has an explicit call to `__wasm_call_ctors`, indicating code not expecting new-style command support. This change does mean that wasm-ld no longer supports DCE-ing the `__wasm_call_ctors` function when there are no calls to it. If there are no calls to it, and there are ctors present, we assume it's wasm-ld's job to insert the calls. This seems ok though, because if there are ctors present, the program is expecting them to be called. This change affects the init-fini-gc.ll test.