Merge pull request #430 from erlang-lager/function-name-otp-18-compat

Take a stab at OTP 18 compatability with macro logging

rebar.config

@@ -22,6 +22,8 @@
 {erl_opts, [
     {lager_extra_sinks, ['__lager_test_sink']},
     {platform_define, "(19|20)", test_statem},
+    {platform_define, "(18)", 'FUNCTION_NAME', unavailable},
+    {platform_define, "(18)", 'FUNCTION_ARITY', 0},
     debug_info,
     report,
     verbose,