Raise required meson version
Review Request #476 — Created Feb. 4, 2021 and submitted
meson was warning:
WARNING: Project specifies a minimum meson_version '>=0.37.0' but uses
features which were added in newer versions:
* 0.40.0: {'build_by_default arg in build target'}
* 0.41.0: {'variables arg in pkgconfig.generate'}
With this change, meson does not show the warning.
