osdep/mac/meson.build: dynamically add features to swift build flags

similar to how our config.h is created the feature flags added to the
swift build should be generated from our features array, instead of
manually adding those when needed.

this prevents errors when forgetting to add any needed flags or remove
obsolete ones.

osdep/mac/meson.build

@@ -17,29 +17,11 @@ if get_option('optimization') != '0'
     swift_flags += '-O'
 endif
 
-if macos_10_15_4_features.allowed()
-    swift_flags += ['-D', 'HAVE_MACOS_10_15_4_FEATURES']
-endif
-
-if macos_11_features.allowed()
-    swift_flags += ['-D', 'HAVE_MACOS_11_FEATURES']
-endif
-
-if macos_12_features.allowed()
-    swift_flags += ['-D', 'HAVE_MACOS_12_FEATURES']
-endif
-
-if macos_cocoa_cb.allowed()
-    swift_flags += ['-D', 'HAVE_MACOS_COCOA_CB']
-endif
-
-if macos_touchbar.allowed()
-    swift_flags += ['-D', 'HAVE_MACOS_TOUCHBAR']
-endif
-
-if macos_media_player.allowed()
-    swift_flags += ['-D', 'HAVE_MACOS_MEDIA_PLAYER']
-endif
+foreach feature, allowed: features
+    if allowed
+        swift_flags += ['-D', 'HAVE_@0@'.format(feature.underscorify().to_upper())]
+    endif
+endforeach
 
 extra_flags = get_option('swift-flags').split()
 swift_flags += extra_flags