EM_JS and function pointers

Our argument name parsing is too simple to support inline function pointer signatures
https://github.com/emscripten-core/emscripten/blob/1488c44c521c3d312028a81cf314ed6c8562b2c9/emscripten.py#L2449

```c++
EM_JS(void, fails, (int (f*)(int)), {...});

#define workaround_arg int (f*)(int)
EM_JS(void, workaround_A, (workaround_arg), {...});

typedef int (F_ii*)(int);
EM_JS(void, workaround_B, (F_ii f), {...});
```

The first one gets the wrong argument name, the second is clunky. Ideally this would just work, but would require either more clever parsing in emscripten.py, or tighter integration with Clang (possibly via a plugin?)