38a1a9b broke `t/xml.c` due to `macros.h` requiring `wlr/version.h`.
This commit fixes it by adding `wlroots` as a direct dependency of the
test executables.
For example, the following node:
<keybind name.action="ShowMenu" menu.action="root-menu"
x.position.action="1" y.position.action="2" />
is converted to:
<keybind>
<action>
<name>ShowMenu</name>
<menu>root-menu</menu>
<position>
<x>1</x>
<y>2</y>
</position>
</action>
</keybind>
...before processing the entire xml tree. This is a preparation to prevent
breaking changes when we refactor rcxml.c to use recursion instead of
encoding nodes into dotted strings.
