[embedded] Update wording on 'no existentials' diagnostic

Author: kubamracek

include/swift/AST/DiagnosticsSIL.def

@@ -353,9 +353,9 @@ ERROR(global_must_be_compile_time_const,none,
 ERROR(non_final_generic_class_function,none,
       "classes cannot have non-final generic fuctions in embedded Swift", ())
 ERROR(embedded_swift_existential_type,none,
-      "Existential type %0 is unavailable in embedded Swift", (Type))
+      "using values of protocol type %0 is not allowed in embedded Swift", (Type))
 ERROR(embedded_swift_existential,none,
-      "Existentials are unavailable in embedded Swift", ())
+      "using values of protocol types is not allowed in embedded Swift", ())
 NOTE(performance_called_from,none,
       "called from here", ())
 

test/embedded/anyobject-error-no-stdlib.swift

@@ -13,6 +13,6 @@ public typealias AnyObject = Builtin.AnyObject
 precedencegroup AssignmentPrecedence { assignment: true }
 
 public func foo(_ x: AnyObject) {
-  _ = type(of: x) // expected-error {{Existential type 'AnyObject' is unavailable in embedded Swift}}
+  _ = type(of: x) // expected-error {{using values of protocol type 'AnyObject' is not allowed in embedded Swift}}
   // expected-note@-1 {{called from here}}
 }

test/embedded/basic-errors-no-stdlib.swift

@@ -4,6 +4,6 @@ public protocol Player {}
 struct Concrete: Player {}
 
 public func test() -> any Player {
-  Concrete() // expected-error {{Existential type 'any Player' is unavailable in embedded Swift}}
+  Concrete() // expected-error {{using values of protocol type 'any Player' is not allowed in embedded Swift}}
   // expected-note@-1 {{called from here}}
 }

test/embedded/throw-trap.swift

@@ -23,7 +23,7 @@ public func catching1() {
   }
 }
 
-// CHECK-EXISTENTIALS: error: Existential type 'any Error' is unavailable in embedded Swift
+// CHECK-EXISTENTIALS: error: using values of protocol type 'any Error' is not allowed in embedded Swift
 
 // CHECK-TRAPS-SIL:      sil @$s4main9throwing1SiyKF : $@convention(thin) () -> (Int, @error any Error) {
 // CHECK-TRAPS-SIL-NEXT: bb0: