Support Darwin environment on buildroot/bin (#10751)

buildroot/bin/opt_enable

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+SED=$(which gsed || which sed)
+
 for opt in "$@" ; do
-  eval "sed -i 's/\/\/[[:blank:]]*\(#define \b${opt}\b\)/\1/g' Marlin/Configuration.h"
+  eval "${SED} -i 's/\/\/[[:blank:]]*\(#define \b${opt}\b\)/\1/g' Marlin/Configuration.h"
 done