We can leave the relative paths to other books (e.g. '../glib' or
'../ModemManager') because running gtkdoc-rebase seems to be broken
since the 1.29 release, see:
https://gitlab.gnome.org/GNOME/gtk-doc/-/issues/138
Remove the need to run `gtkdocize' when building from git; this should
be an operation done by the maintainer when modernizing the gtk-doc
setup (think of e.g. gettextize), no need to do it unconditionally.
This makes it easier for platforms without gtk-doc to build from git.
When trying to build with documentation enabled and gtk-doc isn't
found, we get some nice warnings and errors in the configure report:
checking for gtk-doc... no
configure: WARNING:
You will not be able to create source packages with 'make dist'
because gtk-doc >= 1.0 is not found.
checking for gtkdoc-check... no
checking for gtkdoc-check... no
checking for gtkdoc-rebase... no
checking for gtkdoc-mkpdf... no
checking whether to build gtk-doc documentation... yes
configure: error:
You must have gtk-doc >= 1.0 installed to build documentation for
ModemManager. Please install gtk-doc or disable building the
documentation by adding '--disable-gtk-doc' to './configure'.
Files generated with gtkdocize (gtk-doc) 1.25.1.
