[BitwiseCopyable] Loosen validation assertion.

Don't verify triviality of a suppressed conformance.

Author: nate-chandler

lib/SIL/IR/TypeLowering.cpp

@@ -3203,7 +3203,8 @@ void TypeConverter::verifyTrivialLowering(const TypeLowering &lowering,
     }
   }
 
-  if (!lowering.isTrivial() && conformance) {
+  if (!lowering.isTrivial() && conformance &&
+      !conformance.hasUnavailableConformance()) {
     // A non-trivial type can have a conformance in a few cases:
     // (1) containing or being a conforming archetype
     // (2) is resilient with minimal expansion

test/SILGen/bitwise_copyable.swift

@@ -51,3 +51,11 @@ func pass(_ e: E) { take(e) }
 func opacify() -> some _BitwiseCopyable {
     return Int()
 }
+
+struct NeverGoingToBeBitwiseCopyable {
+  var a: AnyObject
+}
+
+@available(*, unavailable)
+extension NeverGoingToBeBitwiseCopyable : _BitwiseCopyable {
+}