Teach the ClangImporter About Mac Catalyst Availability

Add some missing definitions for the mac catalyst platform. This enables the importing of macCatalyst platform availability attributes.

Author: CodaFi

lib/ClangImporter/ClangImporter.cpp

@@ -2177,9 +2177,10 @@ bool PlatformAvailability::isPlatformRelevant(StringRef name) const {
     return name == "ios" || name == "ios_app_extension";
 
   case PlatformKind::macCatalyst:
+    return name == "ios" || name == "maccatalyst";
   case PlatformKind::macCatalystApplicationExtension:
-    // ClangImporter does not yet support macCatalyst.
-    return false;
+    return name == "ios" || name == "ios_app_extension" ||
+           name == "maccatalyst" || name == "maccatalyst_app_extension";
 
   case PlatformKind::tvOS:
     return name == "tvos";

lib/ClangImporter/ImportDecl.cpp

@@ -9083,9 +9083,12 @@ void ClangImporter::Implementation::importAttributes(
         llvm::StringSwitch<Optional<PlatformKind>>(Platform)
           .Case("ios", PlatformKind::iOS)
           .Case("macos", PlatformKind::macOS)
+          .Case("maccatalyst", PlatformKind::macCatalyst)
           .Case("tvos", PlatformKind::tvOS)
           .Case("watchos", PlatformKind::watchOS)
           .Case("ios_app_extension", PlatformKind::iOSApplicationExtension)
+          .Case("maccatalyst_app_extension",
+                PlatformKind::macCatalystApplicationExtension)
           .Case("macos_app_extension",
                 PlatformKind::macOSApplicationExtension)
           .Case("tvos_app_extension",