The Debian and GNU architecture names match very often, even though
there are common cases (32-bit Arm or 64-bit x86) where they do not
and other cases in which the GNU triplet is actually a quadruplet.
But it is still possible to group the common case into a single
case inside probe_target_compiler.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>