backend-vnc: support building aml and neatvnc as subprojects
Building aml and neatvnc as subprojects requires Meson 0.63 for its per-subproject compiler options due to the different c_std
.
This bumps the required Meson version to 0.63, adds support to build aml and neatvnc as subprojects, and adds wrap files so they can be checked out with meson subprojects download
.
Edited by Philipp Zabel