From what I can find, this is a bug in xcb/proto's py-compile. It apparently is no-longer appropriate to fail due to an empty --destdir argument, https://lists.gnu.org/archive/html/automake-patches/2011-06/msg00056.html http://debbugs.gnu.org/cgi/bugreport.cgi?bug=11762 (problem found in git master)
Can't reproduce after git clean -xfd, closing.
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