In a preBuildCommands/postBuildCommands, how do I invoke an application
that was specified as a dependency?

Ie, suppose I have two DUB packages: "MyApp" and "SomeTool", where
"SomeTool" is specified as a dependency of "MyApp". To build "MyApp", I
first need "SomeTool" to be built and then invoked. Note also that
"SomeTool" doesn't already exist on the user's PATH.