bpo-36642: make unicodedata const (GH-12855)

diff --git a/Tools/unicode/makeunicodedata.py b/Tools/unicode/makeunicodedata.py
index 9327693..2550b8f 100644
--- a/Tools/unicode/makeunicodedata.py
+++ b/Tools/unicode/makeunicodedata.py
@@ -1249,7 +1249,7 @@
         size = getsize(self.data)
         if trace:
             print(self.name+":", size*len(self.data), "bytes", file=sys.stderr)
-        file.write("static ")
+        file.write("static const ")
         if size == 1:
             file.write("unsigned char")
         elif size == 2: