When made a soft link of `protoc-erl` (e.g. ln -s PATH/gpb/bin/protoc-erl /usr/local/bin, add protoc-erl in $PATH),
When made a soft link of `protoc-erl`
(e.g. ln -s PATH/gpb/bin/protoc-erl /usr/local/bin,
add protoc-erl in $PATH),

There will be error occurred due to the wrong path.
So I add a link file check for handle this case.

mmmries/gpb