Build warnings in template for intervaltree.pxi 
The `scalar_t` fused type https://github.com/pandas-dev/pandas/blob/b115a6bf5553445fdf29824623ea2b7c3a424660/pandas/_libs/intervaltree.pxi.in#L9-L14 mixes signed and unsigned types. Later on, the code does comparisons with unsigned types, which creates a bunch of compiler warning. 

xref http://docs.cython.org/en/latest/src/userguide/fusedtypes.html#type-checking-specializations

From comments in #27157 it appears there's no established guideline on how different cases for different types should look like in the templates. That's a hindrance to fixing this (and other warnings) as well.