build: simplify by using disabler deps

examples/meson.build

@@ -1,10 +1,10 @@
 threads = dependency('threads')
 wayland_cursor = dependency('wayland-cursor')
-libpng = dependency('libpng', required: false)
+libpng = dependency('libpng', required: false, disabler: true)
 # These versions correspond to ffmpeg 4.0
-libavutil = dependency('libavutil', version: '>=56.14.100', required: false)
-libavcodec = dependency('libavcodec', version: '>=58.18.100', required: false)
-libavformat = dependency('libavformat', version: '>=58.12.100', required: false)
+libavutil = dependency('libavutil', version: '>=56.14.100', required: false, disabler: true)
+libavcodec = dependency('libavcodec', version: '>=58.18.100', required: false, disabler: true)
+libavformat = dependency('libavformat', version: '>=58.12.100', required: false, disabler: true)
 
 # epoll is a separate library in FreeBSD
 if host_machine.system() == 'freebsd'
@@ -13,13 +13,6 @@ else
 	libepoll = []
 endif
 
-# Small hack until https://github.com/mesonbuild/meson/pull/3386/ is merged
-foreach dep : ['libpng', 'libavutil', 'libavcodec', 'libavformat']
-	if not get_variable(dep).found()
-		set_variable(dep, disabler())
-	endif
-endforeach
-
 # Check if libavutil is found because of https://github.com/mesonbuild/meson/issues/6010
 if libavutil.found() and not cc.has_header('libavutil/hwcontext_drm.h', dependencies: libavutil)
 	libavutil = disabler()
@@ -121,18 +114,10 @@ examples = {
 }
 
 foreach name, info : examples
-	all_dep_found = true
-	foreach d : info.get('dep')
-		all_dep_found = all_dep_found and d.found()
-	endforeach
-	if all_dep_found
 	executable(
 		name,
 		info.get('src'),
 		dependencies: info.get('dep'),
 		build_by_default: get_option('examples'),
 	)
-	else
-		warning('Dependencies not satisfied for ' + name)
-	endif
 endforeach

meson.build

@@ -3,7 +3,7 @@ project(
 	'c',
 	version: '0.8.1',
 	license: 'MIT',
-	meson_version: '>=0.48.0',
+	meson_version: '>=0.49.0',
 	default_options: [
 		'c_std=c11',
 		'warning_level=2',