GNU make yields "commands commence before first target" error

First of all, you are looking at the contents of a variable that is named after the current path, which is probably not what you want. A simple environment variable reference is $(name) or ${name}, not $(${name}). Due to this, line 13 is always evaluated.

Second, I think it is choking on the indentation of the $(error ...) expression. While the expression resolves to an empty string, there is still a tab character at the start of the line, which indicates a command, which in turn cannot exist outside a rule.

I think using spaces rather than tabs to indent would work.

When you get Make error messages, always check the Error message documentation

On GNU Make 3.81 (error appears to have been removed from newer versions), it says:

This means the first thing in the makefile seems to be part of a command script: it begins with a TAB character and doesn't appear to be a legal make command (such as a variable assignment). Command scripts must always be associated with a target.

What makes matters more confusing is that "doesn't appear to be a legal make command" part. That explains why in:

    a := b
    $(error a)

the error happens at line 2 and not 1: make simply accepts statements that it can parse, like the assignment, so the following works:

    a := b
a:
    echo $a

Note: SO currently converts tabs to spaces in code, so you can't just copy the above code into your editor.