[IRGen] Ensure that empty structs respect non-trivial destruction of members

An empty struct that is noncopyable can nonetheless have a `deinit`, so
it is not trivially destructible. In such cases, embedded them in
another empty struct means that the outer struct should also not be
trivially destructible. Make it so.

(cherry picked from commit b19a325)

Author: DougGregor

lib/IRGen/StructLayout.cpp

@@ -178,10 +178,10 @@ StructLayout::StructLayout(IRGenModule &IGM, std::optional<CanType> type,
       SpareBits.clear();
       IsFixedLayout = true;
       IsLoadable = true;
-      IsKnownTriviallyDestroyable = deinit;
-      IsKnownBitwiseTakable = IsBitwiseTakable;
-      IsKnownAlwaysFixedSize = IsFixedSize;
-      IsKnownCopyable = copyable;
+      IsKnownTriviallyDestroyable = deinit & builder.isTriviallyDestroyable();
+      IsKnownBitwiseTakable = builder.isBitwiseTakable();
+      IsKnownAlwaysFixedSize = builder.isAlwaysFixedSize();
+      IsKnownCopyable = copyable & builder.isCopyable();
       Ty = (typeToFill ? typeToFill : IGM.OpaqueTy);
     } else {
       MinimumAlign = builder.getAlignment();

test/IRGen/moveonly_deinits.swift

@@ -373,3 +373,18 @@ public func testKlassEnumPairWithDeinit() {
         consumeKlassEnumPairWithDeinit(f)
     }
 }
+
+struct EmptyMoveOnlyWithDeinit: ~Copyable {
+  deinit {}
+}
+
+struct EnclosesEmptyMoveOnlyWithDeinit: ~Copyable {
+  var stored: EmptyMoveOnlyWithDeinit
+}
+
+// IR-LABEL: define {{.*}}swiftcc void @"$s16moveonly_deinits35testEnclosesEmptyMoveOnlyWithDeinityyF"()
+func testEnclosesEmptyMoveOnlyWithDeinit() {
+  // CHECK-NOT: ret
+  // CHECK: call swiftcc void @"$s16moveonly_deinits23EmptyMoveOnlyWithDeinitVfD"()
+  _ = EnclosesEmptyMoveOnlyWithDeinit(stored: EmptyMoveOnlyWithDeinit())
+}