[stdlib] Make the stringForPrintObject function not inlined by default.

Inlining it causes the lldb "po" command to generate a 50KB binary blob that
needs to be injected into the target process.  It is much faster to just call
into the standard-library binary.

<rdar://problem/27710066>

Author: scallanan

stdlib/public/core/DebuggerSupport.swift

@@ -283,7 +283,7 @@ public enum _DebuggerSupport {
     }
   }
 
-  public static func stringForPrintObject(_ value: Any) -> String {
+  @_semantics("stdlib_binary_only") public static func stringForPrintObject(_ value: Any) -> String {
     var maxItemCounter = Int.max
     var refs = Set<ObjectIdentifier>()
     var targetStream = ""