This means you can have one gcc version for some gcc recipes
(e.g. crosssdk/nativesdk) and another gcc version for target code.
Also remove the preferred version entry from the default toolchains
list since the version issue is now handled automatically.
We also need to specifically handle gcc-source in the license handling
code since expanding ${PV} in the base class isn't possible. Since
gcc-source doesn't generate any packages directly this shouldn't be
an issue and whitelisting in this way is easiest (and matches the
rest of the toolchain handling).
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
