Merge pull request #34565 from slavapestov/conformance-availability-part1

Sema: (Mostly) check conformance availability

include/swift/Basic/LangOptions.h

@@ -95,6 +95,9 @@ namespace swift {
     /// Disable API availability checking.
     bool DisableAvailabilityChecking = false;
 
+    /// Should conformance availability violations be diagnosed as errors?
+    bool EnableConformanceAvailabilityErrors = false;
+
     /// Maximum number of typo corrections we are allowed to perform.
     /// This is disabled by default until we can get typo-correction working within acceptable performance bounds.
     unsigned TypoCorrectionLimit = 0;