Support MacOS SDK version 10.12

This adds the new macOS SDK version to the supported version list.
Surprisingly it simply works like this.
Test: make adb aapt

Change-Id: Ic72cee7345b5f49b6a743c70bd266866a06bc459
diff --git a/cc/config/x86_darwin_host.go b/cc/config/x86_darwin_host.go
index 09418c7..b17395d 100644
--- a/cc/config/x86_darwin_host.go
+++ b/cc/config/x86_darwin_host.go
@@ -89,6 +89,7 @@
 		"10.9",
 		"10.10",
 		"10.11",
+                "10.12",
 	}
 
 	darwinAvailableLibraries = append(