build error when building doc is disabled

[Nicolas CARRIER]

Hello,
In the current HEAD (62c37fa), if I disable the doc at configure time, then the 
configure fails.

here are the steps to reproduce :

git clone git://github.com/tgraf/libnl.git
cd libnl
./autogen.sh
mkdir build install
cd build
../configure --prefix=$(realpath ../install) --disable-doc

I'm far from being an autotools guru so I couldn't find a fix for that.

Do you know how to fix this ? And in the first place, why is the doc/ configure 
script ran, although doc building was disabled ?

Thank you in advance.