Fix issues related to using a modern version of the PSP toolchain (#3 )

* Allow PSPDEV to point outside the repo

* Proper support for DEBUG and OE target variants

* Fix build issues related to GCC 9.3.0

* Be more aggressive about stripping the binary

Cut out <iostream> to get ~400kB of locale tables back when using GCC 9.3.0

* Add CI caching + latest-pspdev job

* Fix typo in the latest-pspdev CI job

* Update SEARCH_DIR in linkfile.prx

bd14844