$PKG_CONFIG_LIBDIRS set incorrectly when building open-ocd

I'm running a boxen based mac, not sure if that matters, but I'm testing in a non-standard environment.

When compiling open-ocd from the repositories it didn't find my libusb1, even though it was installed through brew. I had to edit the super environment to get my $PKG_CONFIG_LIBDIRS working properly. I'm new to Homebrew so I'm not sure if I'm taking the right approach.