The main advantage is when targeting sway/wayland instead of i3/x11;
sway doesn't package ipc.h. There *is* an ipc.h in the sway sources,
but it doesn't define e.g the header format, and has different names
for the constants.
There's no pkg-config file shipped with i3, so our only option is to
manually look for the file (and assume it can be found in the "normal"
include paths).
Module plugins are (still) built in <build-dir>/modules.
When installing, f00bar binary is installed to <install-dir>/bin, and
the module plugins to <install-dir>/lib/f00bar.
For this to work, we now also set RPATH correctly. Since the installed
module plugins end up in a different location then when building,
different settings is required for BUILD_RPATH and INSTALL_RPATH.
TODO: optimizations and proper cleanup
* We currently reload the shared library for each *instance* of the
module, and we do it twice; once when verifying, and once when
instantiating.
* The shared libraries are never dlclosed()
