tcmode: add SDKGCCVERSION bits

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
tcmode: kill the TOOLCHAIN_HOST_TASK override

This means we won't be able to build meta-toolchain with an external
toolchain, but it does mean we don't screw up buildtools-tarball. If we need
a functional meta-toolchain in the future, we can resurrect a superior
implementation of this.

Signed-off-by: Christopher Larson <chris_larson@mentor.com>