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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<tr><td><span title='2020-12-11 21:37:07 +0100'>2020-12-11</span></td><td><a href='/guix/commit/gnu/installer/substitutes.scm?id=8361817bf693742757b096468198626f297bb09e'>install: Discover local substitute servers.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>