WebAssembly tail-call proposal has advanced to Phase 4

When compiling C/C++ code, that can be enabled with -mcpu=generic+tail_call:

    zig cc -s -Os --target=wasm32-wasi -mcpu=generic+tail_call app.c

The bulk memory proposal is already activated by default in most runtimes, so that can be enabled as well:

    zig cc -s -Os --target=wasm32-wasi -mcpu=generic+bulk_memory+tail_call app.c