Fix compilation warnings (#27371)

Author: pilkibun

pandas/_libs/internals.pyx

@@ -382,7 +382,7 @@ def get_blkno_indexers(int64_t[:] blknos, bint group=True):
 
         object blkno
         list group_order
-        dict group_slices
+        dict group_dict
         int64_t[:] res_view
 
     n = blknos.shape[0]

pandas/_libs/tslibs/c_timestamp.pyx

@@ -213,7 +213,7 @@ cdef class _Timestamp(datetime):
 
     def __add__(self, other):
         cdef:
-            int64_t other_int, nanos
+            int64_t other_int, nanos = 0
 
         if is_timedelta64_object(other):
             other_int = other.astype('timedelta64[ns]').view('i8')

pandas/_libs/window.pyx

@@ -1682,7 +1682,7 @@ def roll_window(ndarray[float64_t, ndim=1, cast=True] values,
     Assume len(weights) << len(values)
     """
     cdef:
-        ndarray[float64_t] output, tot_wgt, counts
+        float64_t[:] output, tot_wgt, counts
         Py_ssize_t in_i, win_i, win_n, in_n
         float64_t val_in, val_win, c, w