Don't add ${tag}/bin to the $PATH
While the effect to add the meson/ninja/cmake versions used by PackageBuild available to the user is nice when you want to debug a CMake/Meson based package, it is also an unwanted thing when you call setup.[sh|csh] in order to just use the compiled applications.
A better solution would be to define in PackageBuild a pb_tools
action that can be executed by the user when he wants to use CMake, Meson or Ninja.