tools: make genv8constants.py Python3-compatible

PR-URL: #37835
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/genv8constants.py

@@ -73,6 +73,7 @@ def out_define():
   out_reset()
 
 for line in pipe:
+  line = line.decode('utf-8')
   if curr_sym != None:
     #
     # This bit of code has nasty knowledge of the objdump text output