[gentoo-alt] Is it recommendable to prepend the PKG_CONFIG_PATH?

When trying to emerge x11-libs/vte in a prefix tree I get a failure
because the package requires a sufficiently recent glib.

I can work myself around this by declaring

  export PKG_CONFIG_PATH=$EPREFIX/usr/lib/pkgconfig:$PKG_CONFIG_PATH
  export PKG_CONFIG_PATH=$EPREFIX/usr/share/pkgconfig:$PKG_CONFIG_PATH

Is this in fact something that would be recommendable to do all the time?

If so, at which point in the bootstrapping sequence?

And, are there more "pkgconfig" directories besides the two that I have
found?

--Rabbe Fogelholm