[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
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