$(call if_changed_dep,cpp_lds_S) is cpp_lds_S the argument for if_changed_dep? what on earth iis it? a command or argumebnt?

I apologize for the confusion in my previous response. `cpp_lds_S` is actually the command that is being passed as an argument to the `if_changed_dep` function in the expression `$(call if_changed_dep,cpp_lds_S)`.

The `if_changed_dep` function is a built-in function in Makefile that is used to run a command only if its dependencies have changed. The syntax for using `if_changed_dep` is:

$(if_changed_dep,command)

Here, `command` is the shell command that you want to run if its dependencies have changed.

In your example, `cpp_lds_S` is being passed as a command argument to `if_changed_dep`. This means that `cpp_lds_S` is the command that will be executed by `if_changed_dep` if its dependencies have changed.

So, the `if_changed_dep` function will check if the dependencies of the target that is being built have changed since the last build, and if they have, it will execute the `cpp_lds_S` command. If the dependencies have not changed, `cpp_lds_S` will not be executed.

I apologize for any confusion caused by my earlier response.