The file $(top_srcdir)/gtk-doc.make doesn't exist, so don't include it.

--- a/doc/Makefile.in	2007-04-08 20:17:25.000000000 +0200
+++ b/doc/Makefile.in	2014-09-06 23:19:41.413397662 +0200
@@ -240,9 +240,6 @@
 distclean-generic clean-generic maintainer-clean-generic clean \
 mostlyclean distclean maintainer-clean
 
-
-include $(top_srcdir)/gtk-doc.make
-
 # Tell versions [3.59,3.63) of GNU make to not export all variables.
 # Otherwise a system limit (for SysV at least) may be exceeded.
 .NOEXPORT:
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<div class='path'>path: <a href='/guix/log/?id=aaf4b08c6bc2f17b500576dc1676ce1e2c010b19'>root</a>/<a href='/guix/log/tests?id=aaf4b08c6bc2f17b500576dc1676ce1e2c010b19'>tests</a>/<a href='/guix/log/tests/upstream.scm?id=aaf4b08c6bc2f17b500576dc1676ce1e2c010b19'>upstream.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/tests/upstream.scm?id=aaf4b08c6bc2f17b500576dc1676ce1e2c010b19&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-01-05 21:17:58 +0100'>2022-01-05</span></td><td><a href='/guix/commit/tests/upstream.scm?id=6226df77ee7448ba4eae05c14aa2ba9721f28bb4'>tests: Add failing tests for changed-inputs on new style inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/upstream.scm ("changed-inputs returns changes to plain input list",
"changed-inputs returns changes to all plain input lists"): New tests.
</span></span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2022-01-05 21:17:54 +0100'>2022-01-05</span></td><td><a href='/guix/commit/tests/upstream.scm?id=a6bf1c108ef3b0d63d6d6070b90093bc8f434734'>tests: Add tests for changed-inputs on old-style inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>All these tests pass, because they only test the old-style input alists with
labels.

* tests/upstream.scm ("changed-inputs returns no changes",
"changed-inputs returns changes to labelled input list",
"changed-inputs returns changes to all labelled input lists"): New tests.
</span></span></td><td>Ricardo Wurmus</td></tr>