Do not introduce timestamps in PNG files (for icons).
See <https://wiki.debian.org/ReproducibleBuilds/TimestampsInPNG>.

--- awesome-3.4.15/CMakeLists.txt	2013-02-11 14:50:21.000000000 +0100
+++ awesome-3.4.15/CMakeLists.txt	2016-06-16 13:59:30.528125439 +0200
@@ -295,7 +295,7 @@ macro(a_icon_convert match replacement i
         set(ALL_ICONS ${ALL_ICONS} ${output})
 
         add_custom_command(
-            COMMAND ${CONVERT_EXECUTABLE} ${input} ${ARGN} ${output}
+            COMMAND ${CONVERT_EXECUTABLE} +set date:create +set date:modify -define png:exclude-chunk=time ${input} ${ARGN} ${output}
             OUTPUT  ${output}
             DEPENDS ${input}
             VERBATIM)
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<tr><td><span title='2021-06-24 02:29:13 +0200'>2021-06-24</span></td><td><a href='/guix/commit/gnu/packages/pascal.scm?id=67b682f0ba10ca7aaf8ca5fc6a6ce4baf86b7d19'>gnu: fpc: Update to 3.2.2.</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2020-12-19 16:06:03 +0100'>2020-12-19</span></td><td><a href='/guix/commit/gnu/packages/pascal.scm?id=ef7eaeedc029fa6458bd573133dde97c6a452c23'>gnu: fpc: Use HTTPS home page URI.</a><span class='msg-avail'>...</span></td><td>Nicolas Goaziou</td></tr>
<tr><td><span title='2020-09-04 09:33:13 -0500'>2020-09-04</span></td><td><a href='/guix/commit/gnu/packages/pascal.scm?id=46daff38bc2ce03d28480fa7a479c5c51e61001f'>gnu: fpc: Fix reproducibility problem.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2020-08-29 21:44:51 +0200'>2020-08-29</span></td><td><a href='/guix/commit/gnu/packages/pascal.scm?id=6d69886d73cc65a9ca90b482feba299799a8f51e'>gnu: Add p2c.</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2020-08-29 21:20:05 +0200'>2020-08-29</span></td><td><a href='/guix/commit/gnu/packages/pascal.scm?id=fae995d309be226c793e77241cbb7f2c8a0800a6'>gnu: Add fpc.</a><span class='msg-avail'>...</span></td><td>Kei Kebreau</td></tr>