Fix signature of initObjToJSON
This patch is required to make Pandas compile with `-Wl,--fatal-warnings`. It is also needed to prevent an "indirect call signature mismatch" error when using pandas in wasm. This is the only patch Pyodide currently applies to Pandas.
Strange. Does this line not need to change too?

https://github.com/pandas-dev/pandas/blob/45f094d1fdbda6d09954dd49f72bebfeebf0de3b/pandas/_libs/src/ujson/python/ujson.c#L46 Sorry misread that. This lgtm For the record the error we get without this is:
```
wasm-ld: error: function signature mismatch: initObjToJSON
>>> defined as () -> void in build/temp.emscripten_3_1_13_wasm32-cpython-310/pandas/_libs/src/ujson/python/ujson.o
>>> defined as () -> i32 in build/temp.emscripten_3_1_13_wasm32-cpython-310/pandas/_libs/src/ujson/python/objToJSON.o
``` Thanks @hoodmane 