aedi: add initialize method to target class

it's called on all targets except selected one before prefix directory creation

aedi/builder.py

@@ -72,6 +72,10 @@ class Builder(object):
             state.external_source = True
             self._detect_target()
 
+        for target in self._targets.values():
+            if target != self._target:
+                target.initialize(state)
+
         del self._targets
 
         if arguments.build_path:

aedi/target/base.py

@@ -48,6 +48,9 @@ class Target:
     def prepare_source(self, state: BuildState):
         pass
 
+    def initialize(self, state: BuildState):
+        pass
+
     def detect(self, state: BuildState) -> bool:
         return False