fixup ov
target-ppc: Use add2 for carry generation

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-ppc: Implement neg in terms of subf

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-optimize: Fold sub r,0,x to neg r,x

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-ppc: Compute arithmetic shift carry without branches

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-ppc: Compute mullwo without branches

Signed-off-by: Richard Henderson <rth@twiddle.net>