bug#15640: make failure when creating bootstrap-graph.png

[Eric Bavier]

Hello Guix,

>From a fresh checkout of the guix source, a vpath build fails when
trying to create doc/images/bootstrap-graph.png:

$ git clone git://git.savannah.gnu.org/guix.git
[...]
$ cd guix && ./bootstrap
[...]
$ mkdir build && cd build && ../configure
[...]
$ make
[...]
/bin/bash /tmp/guix/build-aux/missing dot -Tpng -Gratio=.9 -Gnodesep=.005 
-Granksep=.00005 -Nfontsize=9 -Nheight=.1 -Nwidth=.1 < 
"../doc/images/bootstrap-graph.dot" > "doc/images/bootstrap-graph.png.tmp"
/bin/bash: doc/images/bootstrap-graph.png.tmp: File or directory not found
Makefile:3318: recipe for target 'doc/images/bootstrap-graph.png' failed
make[2]: *** [doc/images/bootstrap-graph.png] Error 1
$ ls doc
$ mkdir doc/images
$ make
[...]
$ echo $?
0

After configure I don't see a "doc" directory, so it's being created at
some point, but it looks like the doc/images directory isn't being
created before make wants to put bootstra-graph.png there.

I don't recall running into this problem a couple days ago.

-- 
`~Eric