cross-canadian: Handle powerpc linux verses linux-gnuspe

cross-canadian: Handle powerpc linux verses linux-gnuspe

PowerPC toolchains can use the OS "linux" or "linux-gnuspe". This
patch links them together so the one cross-canadian toolchain can support
both.

GCC_FOR_TARGET is set for the GCC recipe as otherwise configure
can pick up an incorrect value.

[YOCTO #5354]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Saul Wold <sgw@linux.intel.com>