Change retroarch configure options

according to this thread http://www.raspberrypi.org/phpBB3/viewtopic.php?f=78&t=56070
picodrive: make clean, compile new sources
pocketsnes: make clean, compile new sources
Update libretrocores.shinc

pcsx_rearmed: make clean, compile new sources
gpsp: remove -Ofast if PI has only 256mb
Various emus: make clean, compile new sources
rpi-update: workaround update issue

http://www.raspberrypi.org/phpBB3/viewtopic.php?t=72587&p=523131
Merge pull request #296 from gizmo98/master

Add make clean to some emus and retrorarch ./configure options