Lower signatures exposing struct registers to byval struct pointers

test/Transforms/NaCl/simplify-struct-reg-pad-crash.ll

+; RUN: not opt < %s -simplify-struct-reg-signatures -S
+
+%struct = type { i32, i32 }
+
+declare i32 @__hypothetical_personality_1(%struct)
+
+declare void @something_to_invoke()
+
+; landingpad with struct
+define void @landingpad_is_struct() {
+  invoke void @something_to_invoke()
+    to label %OK unwind label %Err
+
+OK:
+  ret void
+
+Err:
+  %exn = landingpad i32 personality i32(%struct)* @__hypothetical_personality_1
+      cleanup
+  resume i32 %exn
+}