reuse enum from C definition

Author: MarcoGorelli

pandas/_libs/tslibs/np_datetime.pxd

@@ -9,11 +9,6 @@ from numpy cimport (
 )
 
 
-cdef enum Exact:
-    INEXACT_MATH
-    EXACT_MATCH
-    NO_MATCH
-
 # TODO(cython3): most of these can be cimported directly from numpy
 cdef extern from "numpy/ndarrayobject.h":
     ctypedef int64_t npy_timedelta
@@ -125,3 +120,9 @@ cdef int64_t convert_reso(
     NPY_DATETIMEUNIT to_reso,
     bint round_ok,
 ) except? -1
+
+cdef extern from "src/datetime/np_datetime_strings.h":
+    cdef enum Exact:
+        INEXACT_MATCH
+        EXACT_MATCH
+        NO_MATCH