gcc-cross-wrapper: Explicitly add LD program name.

This is because autoconf is passing -print-prog-name=ld to the
cross-gcc, which in turn assumes a FHS compliant filesystem hierarchy
and searches ../../../../$crossConfig/bin/ld for the correct ld.

Of course, this won't work on Nix, hence we're explicitly passing the
correct LD program name.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>