BLD: address build warnings
xref #30609
Nice! Does this address all of them? Not sure if you've seen it, but besides the failure in the docs, this error is happening lots of times in the tests:
```
Exception ignored in: 'pandas._libs.window.aggregations.is_monotonic_start_end_bounds'

TypeError: Argument 'arr' has incorrect type (expected numpy.ndarray, got pandas._libs.window.aggregations._memoryviewslice)
``` > Does this address all of them?

No.  Locally (only checked OSX) it addresses the buffer unpacking in aggregations.pyx and the assignment warnings for algos.c.  The __pyx_memview_get_object ones I think are coming from an unused import; they dont correspond directly to any of the .pyx code > > Does this address all of them?
> 
> No. Locally (only checked OSX) it addresses the buffer unpacking in aggregations.pyx and the assignment warnings for algos.c. The __pyx_memview_get_object ones I think are coming from an unused import; they dont correspond directly to any of the .pyx code

Nice! What's the best way of figuring out what unused import is causing? - For my own knowledge!
`pandas/_libs/hashing.c:25344:20: warning: ‘__pyx_memview_get_object’`

Also I randomly get this warning: (which doesn't seem to be as expected)
```
pandas/_libs/src/ujson/python/objToJSON.c: In function ‘NpyArr_encodeLabels’:
pandas/_libs/src/ujson/python/objToJSON.c:1616:18: warning: ‘len’ may be used uninitialized in this function [-Wmaybe-uninitialized]
```



 > What's the best way of figuring out what unused import is causing? - For my own knowledge!

No idea The one is caused by Cython so can't speak to that but for the JSON one if you look at the line:

https://github.com/pandas-dev/pandas/blob/4206fd42cc5cd20204c0c5f192f7e59f204ad48d/pandas/_libs/src/ujson/python/objToJSON.c#L1616

The warning is saying that there are some code paths where `len` is declared but never assigned, which would give it an undefined value and either give weird results or segfault if that line gets hit without `len` ever having been assigned.

Not clear what path that is though - you are only getting the warning intermittently? Thanks @jbrockmendel 