Fix test and update comment

Even if possible (in metadata) there is no point in setting `final` on
a method if we remove `virtual`. This match ILLink version of the sealer
and makes the same test pass on both.

dotnet/targets/Xamarin.Shared.Sdk.targets

@@ -464,7 +464,7 @@
 			-->
 			<_ExtraTrimmerArgs>$(_ExtraTrimmerArgs) --disable-opt unusedtypechecks</_ExtraTrimmerArgs>
 
-			<!-- if a release build, not using the JIT (macOS) or the interpreter then the sealer optimization can be used -->
+			<!-- If a release build and the app is not extensible (no interpreter or JIT/code-loading for macOS) then the sealer optimization can be used -->
 			<_ExtraTrimmerArgs Condition="'$(_BundlerDebug)' != 'true' And '$(MtouchInterpreter)' == '' And '$(_PlatformName)' != 'macOS'">$(_ExtraTrimmerArgs) --enable-opt sealer</_ExtraTrimmerArgs>
 
 			<!-- We always want the linker to process debug symbols, even when building in Release mode, because the AOT compiler uses the managed debug symbols to output DWARF debugging symbols -->

tests/linker/ios/link all/SealerTest.cs

@@ -75,7 +75,7 @@ public void Final ()
 			// but it can be optimized / sealed as nothing else is (or can) overrides it
 			Assert.True (a.IsFinal, "A");
 			Assert.True (b.IsFinal, "B");
-			Assert.True (c.IsFinal, "C");
+			Assert.False (c.IsFinal, "C"); // devirtualized
 #endif
 		}
 

tools/linker/MonoTouch.Tuner/SealerSubStep.cs

@@ -102,6 +102,7 @@ protected override void Process (TypeDefinition type)
 				// look if this method is an override to existing _marked_ methods
 				if (!AreMarked (bases)) {
 					method.IsVirtual = false;
+					method.IsFinal = false; // since it's not virtual anymore
 #if DEBUG
 					Console.WriteLine ("Devirtualize {0} ({1})", method, ++devirtualize);
 #endif