Add support code for the canadian-cross case.

Add implementation for a candadian build option already
present in crosstool in order to build a cross-compiler
where build != host != target

Signed-off-by: Bart van der Meulen <bartvdrmeulen@gmail.com>

# Compute powerpc-specific values

. "${CT_LIB_DIR}/scripts/build/arch/powerpc-powerpc64.sh-common"