clint: disregard compound literal return

This allows lines like:

return (my_struct_type) {
  .my_int = 5,
  .my_str = ""
};

Thanks to @watk for finding and fixing it!
api/helpers: implement C string to String helper

Use it in buffers.c
Merge branch 'master' into autogen-headers

Conflicts:
	src/nvim/api/helpers.h