BUG: build failure on PyPy in hash functions

[jorisvandenbossche]

The PyPy builds on conda-forge are failing with

    In file included from pandas/_libs/algos.c:663:
    pandas/_libs/src/klib/khash_python.h: In function 'complexobject_hash':
    pandas/_libs/src/klib/khash_python.h:282:38: error: '_PyHASH_IMAG' undeclared (first use in this function)
      282 |     Py_uhash_t combined = realhash + _PyHASH_IMAG * imaghash;
          |                                      ^~~~~~~~~~~~
    pandas/_libs/src/klib/khash_python.h:282:38: note: each undeclared identifier is reported only once for each function it appears in

This seems to be related to #41988 cc @realead