Add %GetUndetectable() test intrinsic and add tests for undetectables.

src/runtime/runtime.h

Index: src/runtime/runtime.h
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index fd92cb6f123374f33e947834731750cb8524c2bf..bc0c4ca4c16351b0f2cfa7ee8f6ed0d92c8a910c 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -581,6 +581,7 @@ namespace internal {
   F(GetOptimizationStatus, -1, 1)             \
   F(UnblockConcurrentRecompilation, 0, 1)     \
   F(GetOptimizationCount, 1, 1)               \
+  F(GetUndetectable, 0, 1)                    \
   F(ClearFunctionTypeFeedback, 1, 1)          \
   F(NotifyContextDisposed, 0, 1)              \
   F(SetAllocationTimeout, -1 /* 2 || 3 */, 1) \