pkg-config: fix pc-path (#3807)
pkg-config: fix pc-path (#3807)

Joining the array _before_ attempting to add new items to it meant that
an exception was raised on macOS, and the final path was added without a
seperator before it on Linux.
rwhogg/homebrew-core,LinuxbrewTestBot/homebrew-core,maxim-belkin/homebrew-core,LinuxbrewTestBot/homebrew-core,Linuxbrew/homebrew-core,rwhogg/homebrew-core,Linuxbrew/homebrew-core,maxim-belkin/homebrew-core