Merge pull request #36030 from slavapestov/fix-float16-availability-on-macos-5.4

stdlib: Float16 needs an @available annotation for macOS [5.4]

Author: slavapestov

stdlib/public/core/FloatingPointTypes.swift.gyb

@@ -1353,7 +1353,7 @@ internal struct _${Self}AnyHashableBox: _AnyHashableBox {
 ${SelfDocComment}
 @frozen
 %  if bits == 16:
-@available(iOS 14, tvOS 14, watchOS 7, *)
+@available(macOS 11, iOS 14, tvOS 14, watchOS 7, *)
 @available(macOS, unavailable)
 @available(macCatalyst, unavailable)
 %  else:

test/IRGen/float16_macos.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-frontend -emit-ir %s -target x86_64-apple-macos10.15 | %FileCheck %s --check-prefix=CHECK10
+// RUN: %target-swift-frontend -emit-ir %s -target x86_64-apple-macos11 | %FileCheck %s --check-prefix=CHECK11
+
+// REQUIRES: OS=macosx
+// REQUIRES: CPU=x86_64
+// UNSUPPORTED: use_os_stdlib
+
+@available(macOS 11, *)
+public struct Float16Wrapper {
+  @available(macOS, unavailable)
+  var x: Float16
+}
+
+// CHECK10-LABEL: @"$ss7Float16VMn" = extern_weak global %swift.type_descriptor
+// CHECK11-LABEL: @"$ss7Float16VMn" = external global %swift.type_descriptor