Build macros cannot be invoked from a macro context. This means it is impossible to use a macro to create a class which will provide build macros for other classes.
It is also disallowed to invoke expression macros in a macro context.
Trivia: Expression macro-in-macro
Prior to Haxe 4, using expression macros inside a macro context was possible. Support was primarily dropped because such code would cause issues with the compiler cache.