BLD: hashtable.pxd is a pxd depends for _join, hashtable, and index (pandas-dev#15218)

Author: jreback

setup.py

@@ -490,13 +490,13 @@ def pxd(name):
     index={'pyxfile': 'index',
            'sources': ['pandas/src/datetime/np_datetime.c',
                        'pandas/src/datetime/np_datetime_strings.c'],
-           'pxdfiles': ['src/util'],
+           'pxdfiles': ['src/util', 'hashtable'],
            'depends': _pxi_dep['index']},
     algos={'pyxfile': 'algos',
-           'pxdfiles': ['src/util'],
+           'pxdfiles': ['src/util', 'hashtable'],
            'depends': _pxi_dep['algos']},
     _join={'pyxfile': 'src/join',
-           'pxdfiles': ['src/util'],
+           'pxdfiles': ['src/util', 'hashtable'],
            'depends': _pxi_dep['_join']},
     _window={'pyxfile': 'window',
              'pxdfiles': ['src/skiplist', 'src/util'],