meson: custom libweston install location

To avoild conflicting with libweston provided by packages, option
'custom-libdir' provides a way to install libweston under a custom location.

Signed-off-by: Xichen Zhou <sichem.zh@gmail.com>
3 jobs for libweston-subpj in 1 minute and 21 seconds (queued for 1 second)
latest
Status Name Job ID Coverage
  Container Prep
passed container_prep #2730828

00:00:26

 
  Build
passed build-native-meson-default-options #2730829

00:00:54

passed build-native-meson-no-gl-renderer #2730830

00:00:34