asn2wrs: use system lex and yacc from ply if available

Tested with python-ply 3.11 and Python 3.7.3 on Arch Linux using the
'ninja asn1' command.

Bundling lex.py and yacc.py is one distribution method suggested by PLY
upstream (https://www.dabeaz.com/ply/README.txt), but since it is also
available in many Linux distributions, we could potentially remove it in
the future. Windows developers can install it through pip if needed.

Change-Id: I9c847072916ee33da49994820b435ec1d7110303
Reviewed-on: https://code.wireshark.org/review/33708
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot
Reviewed-by: Pascal Quantin <pascal@wireshark.org>
Reviewed-by: Peter Wu <peter@lekensteyn.nl>

debian/patches/04_asn2wrs_ply.patch

@@ -1,18 +0,0 @@
-Description: Use lex/yacc from ply
-Forwarded: not-needed
-Bug-Debian: http://bugs.debian.org/554613
-Author: Jakub Wilk <ubanus@users.sf.net>
-
---- a/tools/asn2wrs.py
-+++ b/tools/asn2wrs.py
-@@ -70,8 +70,8 @@
- import getopt
- import traceback
- 
--import lex
--import yacc
-+from ply import lex
-+from ply import yacc
- 
- if sys.version_info[0] < 3:
-     from string import maketrans

debian/patches/series

@@ -1,3 +1,2 @@
-04_asn2wrs_ply.patch
 09_idl2wrs.patch
 16_licence_about_location.patch

tools/asn2wrs.py

@@ -47,8 +47,14 @@ import time
 import getopt
 import traceback
 
-import lex
-import yacc
+try:
+    from ply import lex
+    from ply import yacc
+except ImportError:
+    # Fallback: use lex.py and yacc from the tools directory within the
+    # Wireshark source tree if python-ply is not installed.
+    import lex
+    import yacc
 
 if sys.version_info[0] < 3:
     from string import maketrans