[Reflection] Include TargetConditionals.h for WatchOS detection, not Availability.h.

While we're in there, make SwiftReflectionTest's debugLog function take an @autoclosure so we don't waste a ton of time constructing log messages that are never logged.

Author: mikeash

include/swift/SwiftRemoteMirror/SwiftRemoteMirrorTypes.h

@@ -28,7 +28,7 @@ extern "C" {
 // compatibility. Everywhere else, they are 64-bit so 32-bit processes can
 // potentially read from 64-bit processes.
 #if defined(__APPLE__) && defined(__MACH__)
-#include <Availability.h>
+#include <TargetConditionals.h>
 #if TARGET_OS_WATCH
 #define SWIFT_REFLECTION_NATIVE_POINTERS 1
 #endif

stdlib/private/SwiftReflectionTest/SwiftReflectionTest.swift

@@ -31,9 +31,9 @@ let RequestStringLength = "l"
 let RequestDone = "d"
 let RequestPointerSize = "p"
 
-internal func debugLog(_ message: String) {
+internal func debugLog(_ message: @autoclosure () -> String) {
 #if DEBUG_LOG
-  fputs("Child: \(message)\n", stderr)
+  fputs("Child: \(message())\n", stderr)
   fflush(stderr)
 #endif
 }