python: Use Pattern from typing

Python <3.7 must import Pattern from typing not re

Change-Id: I56acb466aef40b7188e4cd58d3ba5d0b0cc9b090
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42643
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/m5/ext/pystats/group.py

@@ -25,7 +25,7 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 import re
-from typing import Callable, Dict, Iterator, List, Optional, Union
+from typing import Callable, Dict, Iterator, List, Optional, Pattern, Union
 
 from .jsonserializable import JsonSerializable
 from .statistic import Scalar, Statistic
@@ -99,7 +99,7 @@ class Group(JsonSerializable):
         """
         yield from self.children(lambda _name: _name in name)
 
-    def find_re(self, regex: Union[str, re.Pattern]
+    def find_re(self, regex: Union[str, Pattern]
                 ) -> Iterator[Union["Group", Statistic]]:
         """ Find all stats that match the name