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=ea5b0a6fffa49a77cc020e553b49d8f06848229c'>root</a>/<a href='/guix/log/doc?id=ea5b0a6fffa49a77cc020e553b49d8f06848229c'>doc</a>/<a href='/guix/log/doc/images?id=ea5b0a6fffa49a77cc020e553b49d8f06848229c'>images</a>/<a href='/guix/log/doc/images/installer-network.png?id=ea5b0a6fffa49a77cc020e553b49d8f06848229c'>installer-network.png</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/doc/images/installer-network.png?id=ea5b0a6fffa49a77cc020e553b49d8f06848229c&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-03-13 23:12:43 +0100'>2019-03-13</span></td><td><a href='/guix/commit/doc/images/installer-network.png?id=e1c15e8b8e25e14c253ff1212e289565736f6ea7'>doc: Document the graphical installer some more.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>