In out-of-tree builds gtk-doc's setup-build target copies all the content from
$srcdir to $builddir. However, if some of this content is regenerated at
configure time this can happen:
1) configure writes new build/version.xml
2) make compile copies content, including the tarball's src/version.xml
to build/version.xml, and generates gtk-doc.
3) make install notices build/version.xml is older than configure.status,
so regenerates gtk-doc.
gtk-doc generation is a slow process at the best of times, so doing it twice
isn't good.
Signed-off-by: Ross Burton <ross.burton@intel.com>
