add support for building psp toolchain

add support for building psp toolchain

using GCC 4.6.4, binutils 2.23.2, newlib 4.1.0

pspdev repos have GCC 4.6.4, 4.9, 9.3 and latest 11.2 compilers (default)
but since anything > 4.7.4 is written in C++ we'll use gcc 4.6.4 for the
moment. the toolchain works perfectly with pspsdk as of today
(commit cc887d731f635e06fba85118eb5c7ee87746cbc8)

source config/psp464 in your config.sh to build this.
the config uses the new postbuild hook to create symlinks to the binary
names pspsdk expects, and creates a psp-gcc launcher script that has
the right linking order and required libs to build the examples.
i didn't figure out how the official toolchain sets these, but extracted
it from theirs by calling their psp-gcc with -v in a ubuntu sandbox.