NCGenerics: add test for feature flag

Ensure that when using noncopyable generics when building a module,
the compiler can re-ingest it and will pick the part guarded by
$NoncopyableGenerics.

verifies the concern in rdar://127701059

test/ModuleInterface/noncopyable_generics_feature_flag.swift

@@ -0,0 +1,20 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-emit-module-interface(%t/Library.swiftinterface) %t/Library.swift -module-name Library
+// RUN: rm -f %t/Library.swiftmodule
+// RUN: %target-swift-frontend -I %t -typecheck -verify %t/test.swift
+
+
+//--- Library.swift
+
+public struct Hello<T: ~Copyable> {
+  public init() {}
+}
+
+//--- test.swift
+import Library
+
+struct NC: ~Copyable {}
+
+let x: Hello<NC> = .init()