Add 10.13 Mac SDK to whitelist

Add the latest Mac SDK to the version
whitelist.

Test: compilation
Change-Id: I86fcbf2bb100a0af6a2cfea62f524a17ba1a67b9
diff --git a/cc/config/x86_darwin_host.go b/cc/config/x86_darwin_host.go
index 65fa1ed..103f91f 100644
--- a/cc/config/x86_darwin_host.go
+++ b/cc/config/x86_darwin_host.go
@@ -89,6 +89,7 @@
 		"10.10",
 		"10.11",
 		"10.12",
+		"10.13",
 	}
 
 	darwinAvailableLibraries = append(