target/i386: extend cc_* when using them to compute flags

target/i386: extend cc_* when using them to compute flags

Instead of using s->tmp0 or s->tmp4 as the result, just extend the cc_*
registers in place.  It is harmless and, if multiple setcc instructions
are used, the optimizer will be able to remove the redundant ones.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>