SimplifyBuiltin: fix a wrong constant folding of the is_same_metatype builtin for function types

We need to compare the not lowered types, because function types may differ in their original version but are equal in the lowered version, e.g.
```
  ((Int, Int) -> ())
  (((Int, Int)) -> ())
```

Fixes a miscompile

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyBuiltin.swift

@@ -286,7 +286,12 @@ private func typesOfValuesAreEqual(_ lhs: Value, _ rhs: Value, in function: Func
                       rhsExistential.metatype is MetatypeInst
 
   if typesAreExact {
-    if lhsTy == rhsTy {
+    // We need to compare the not lowered types, because function types may differ in their original version
+    // but are equal in the lowered version, e.g.
+    //   ((Int, Int) -> ())
+    //   (((Int, Int)) -> ())
+    //
+    if lhsMetatype == rhsMetatype {
       return true
     }
     // Comparing types of different classes which are in a sub-class relation is not handled by the

test/SILOptimizer/simplify_builtin.sil

@@ -258,11 +258,11 @@ bb0:
   return %4 : $Builtin.Int1
 }
 
-// CHECK-LABEL: sil @different_function_metatype
+// CHECK-LABEL: sil @different_function_metatype1
 // CHECK:         [[R:%.*]] = integer_literal $Builtin.Int1, 0
 // CHECK-NEXT:    return [[R]]
-// CHECK:       } // end sil function 'different_function_metatype'
-sil @different_function_metatype : $@convention(thin) () -> Builtin.Int1 {
+// CHECK:       } // end sil function 'different_function_metatype1'
+sil @different_function_metatype1 : $@convention(thin) () -> Builtin.Int1 {
 bb0:
   %0 = metatype $@thick ((Int) -> Bool).Type
   %1 = metatype $@thick ((Float) -> Bool).Type
@@ -272,6 +272,20 @@ bb0:
   return %4 : $Builtin.Int1
 }
 
+// CHECK-LABEL: sil @different_function_metatype2
+// CHECK:         [[R:%.*]] = builtin "is_same_metatype"
+// CHECK:         return [[R]]
+// CHECK:       } // end sil function 'different_function_metatype2'
+sil @different_function_metatype2 : $@convention(thin) () -> Builtin.Int1 {
+bb0:
+  %0 = metatype $@thick ((Int, Int) -> ()).Type
+  %1 = metatype $@thick (((Int, Int)) -> ()).Type
+  %2 = init_existential_metatype %0 : $@thick ((Int, Int) -> ()).Type, $@thick Any.Type
+  %3 = init_existential_metatype %1 : $@thick (((Int, Int)) -> ()).Type, $@thick Any.Type
+  %4 = builtin "is_same_metatype"(%2 : $@thick Any.Type, %3 : $@thick Any.Type) : $Builtin.Int1
+  return %4 : $Builtin.Int1
+}
+
 // CHECK-LABEL: sil @same_metatype_dynamic_self
 // CHECK:         [[R:%.*]] = integer_literal $Builtin.Int1, -1
 // CHECK-NEXT:    return [[R]]