fix compilation on new versions of MacOS (#100)

Author: mynameisdaniil

README.md

@@ -24,6 +24,8 @@ On MacOS 10.14, to compile `mac_listener`, run:
 open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg
 ```
 
+On newer versions this file doesn't exist. But it still should work just fine as long as you have xcode installed.
+
 ## Usage
 
 Add `file_system` to the `deps` of your mix.exs

mix.exs

@@ -62,7 +62,7 @@ defmodule FileSystem.MixProject do
       ldflags = System.get_env("LDFLAGS", "")
 
       cmd =
-        "clang #{cflags} #{ldflags} -framework CoreFoundation -framework CoreServices -Wno-deprecated-declarations #{source} -o #{target}"
+        "xcrun -r clang #{cflags} #{ldflags} -framework CoreFoundation -framework CoreServices -Wno-deprecated-declarations #{source} -o #{target}"
 
       if Mix.shell().cmd(cmd) > 0 do
         Logger.error(