ensure #if $MoveOnly evaluates to true

I enabled move-only types by default, but I didn't
realize that the `Feature::MoveOnly` needs to graduate
into a `LANGUAGE_FEATURE` so that `EvaluateIfConfigCondition`
will recognize `$MoveOnly` as being true.

fixes rdar://107050387

Author: kavon

include/swift/Basic/Features.def

@@ -98,6 +98,7 @@ SUPPRESSIBLE_LANGUAGE_FEATURE(
     FreestandingExpressionMacros, 382, "Expression macros",
     true)
 LANGUAGE_FEATURE(AttachedMacros, 389, "Attached macros", true)
+LANGUAGE_FEATURE(MoveOnly, 390, "noncopyable types", true)
 
 UPCOMING_FEATURE(ConciseMagicFile, 274, 6)
 UPCOMING_FEATURE(ForwardTrailingClosures, 286, 6)
@@ -108,7 +109,6 @@ EXPERIMENTAL_FEATURE(StaticAssert, false)
 EXPERIMENTAL_FEATURE(VariadicGenerics, false)
 EXPERIMENTAL_FEATURE(NamedOpaqueTypes, false)
 EXPERIMENTAL_FEATURE(FlowSensitiveConcurrencyCaptures, false)
-EXPERIMENTAL_FEATURE(MoveOnly, true)
 EXPERIMENTAL_FEATURE(FreestandingMacros, true)
 
 // FIXME: MoveOnlyClasses is not intended to be in production,

test/ModuleInterface/moveonly_interface_flag.swift

@@ -1,12 +1,10 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-emit-module-interface(%t/Library.swiftinterface) %s -module-name Library -enable-experimental-feature MoveOnly
+// RUN: %target-swift-emit-module-interface(%t/Library.swiftinterface) %s -module-name Library
 // RUN: %target-swift-typecheck-module-from-interface(%t/Library.swiftinterface) -I %t
 // RUN: %FileCheck %s < %t/Library.swiftinterface
 
 // this test makes sure that decls containing a move-only type are guarded by the $MoveOnly feature flag
 
-// CHECK: swift-module-flags-ignorable: -enable-experimental-feature MoveOnly
-
 // CHECK:       #if compiler(>=5.3) && $MoveOnly
 // CHECK-NEXT:    @_moveOnly public struct MoveOnlyStruct {
 
@@ -40,5 +38,3 @@ public class What {
 public extension MoveOnlyStruct {
   func who() {}
 }
-
-

test/Sema/moveonly_experimental.swift

@@ -31,6 +31,14 @@ func checkNoImplicitCopy2(_ x: SomeValue) {
   checkNoImplicitCopy2(y)
 }
 
+// coverage to ensure the feature flag is working
+#if $MoveOnly
+  func guardedFn() {}
+#endif
+
+func caller() {
+  guardedFn()
+}