Fix build with Python 3 scons.

Patch taken from Arch Linux:
https://github.com/archlinux/svntogit-packages/blob/packages/serf/trunk/scons-python3.patch

--- serf-1.3.9/SConstruct.orig	2019-07-26 17:49:30.910189251 +0000
+++ serf-1.3.9/SConstruct	2019-07-26 17:49:54.073821735 +0000
@@ -163,9 +163,9 @@
               suffix='.def', src_suffix='.h')
   })
 
-match = re.search('SERF_MAJOR_VERSION ([0-9]+).*'
-                  'SERF_MINOR_VERSION ([0-9]+).*'
-                  'SERF_PATCH_VERSION ([0-9]+)',
+match = re.search(b'SERF_MAJOR_VERSION ([0-9]+).*'
+                  b'SERF_MINOR_VERSION ([0-9]+).*'
+                  b'SERF_PATCH_VERSION ([0-9]+)',
                   env.File('serf.h').get_contents(),
                   re.DOTALL)
 MAJOR, MINOR, PATCH = [int(x) for x in match.groups()]
@@ -183,7 +183,7 @@
 
 unknown = opts.UnknownVariables()
 if unknown:
-  print 'Warning: Used unknown variables:', ', '.join(unknown.keys())
+  print ('Warning: Used unknown variables:', ', '.join(unknown.keys()))
 
 apr = str(env['APR'])
 apu = str(env['APU'])
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<div class='path'>path: <a href='/guix/log/?id=40bc9c9c42168a91cfa0069234590e8b0a889939'>root</a>/<a href='/guix/log/build-aux?id=40bc9c9c42168a91cfa0069234590e8b0a889939'>build-aux</a>/<a href='/guix/log/build-aux/mdate-from-git.scm?id=40bc9c9c42168a91cfa0069234590e8b0a889939'>mdate-from-git.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/build-aux/mdate-from-git.scm?id=40bc9c9c42168a91cfa0069234590e8b0a889939&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2024-04-19 16:45:41 +0200'>2024-04-19</span></td><td><a href='/guix/commit/build-aux/mdate-from-git.scm?id=2b8a2a6e723a0cf987c814865df9368e6348b6f8'>maint: Generate doc/version[-LANG].texi using `mdate-from-git.scm'.</a><span class='msg-avail'>...<span class='msg-tooltip'>This replaces Automake's `build-aux/mdate-sh' with our own
`build-aux/mdate-from-git.scm' to use reproducible timestamps from Git
instead.

* build-aux/mdate-from-git.scm: New script.
* bootstrap: Use it to replace build-aux/mdate-sh.
* Makefile.am (EXTRA_DIST): Add it.

Change-Id: I17d0a7de9ffea397129c0db1728f86e28a4e245f
</span></span></td><td>Janneke Nieuwenhuizen</td></tr>