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=18d02443e1ec37779ee3cf63f9aaff1746bfdd8e'>root</a>/<a href='/guix/log/gnu?id=18d02443e1ec37779ee3cf63f9aaff1746bfdd8e'>gnu</a>/<a href='/guix/log/gnu/services?id=18d02443e1ec37779ee3cf63f9aaff1746bfdd8e'>services</a>/<a href='/guix/log/gnu/services/sddm.scm?id=18d02443e1ec37779ee3cf63f9aaff1746bfdd8e'>sddm.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/gnu/services/sddm.scm?id=18d02443e1ec37779ee3cf63f9aaff1746bfdd8e&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2024-07-18 10:45:19 +0800'>2024-07-18</span></td><td><a href='/guix/commit/gnu/services/sddm.scm?id=8b5c21269f2191fabf5ecfc4f4d03eb68b04b943'>services: sddm: Adjust pass env.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sddm.scm (sddm-shepherd-service): Adjust pass env when sddm
build with qt6.

Change-Id: Iabaa22824db8048c7c86921010b970226f85b7a5
</span></span></td><td>Zheng Junjie</td></tr>
<tr><td><span title='2024-03-19 18:52:16 +0800'>2024-03-19</span></td><td><a href='/guix/commit/gnu/services/sddm.scm?id=3ea55fada0593cd05c686cef2f6a59ba65933ef5'>services: sddm: Add extension for localed-service-type.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sddm.scm (sddm-service-type): Add extension for
localed-service-type.
* gnu/services/xorg.scm (xorg-configuration-keyboard-layout): Export it.

Change-Id: I26e6475b733d69f1baf00786e302a3ec6d3c4a74
Signed-off-by: 宋文武 &lt;iyzsong@member.fsf.org&gt;
</span></span></td><td>Zheng Junjie</td></tr>
<tr><td><span title='2023-08-02 22:27:43 +0800'>2023-08-02</span></td><td><a href='/guix/commit/gnu/services/sddm.scm?id=7e056197d7bf8f888fe52db9d5ee34ec253ffff9'>services: sddm: Set some environment variables for the breeze theme.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/sddm.scm (sddm-service-type): Pass #:environment-variables to
make-forkexec-constructor.

Signed-off-by: 宋文武 &lt;iyzsong@member.fsf.org&gt;
</span></span></td><td>Zheng Junjie</td></tr>