Add and use is_relation function.
Improved various Cmp-related optimizations.
Improved IR-realization of Mux(x, 0, 1).
Added local optimizations: And(x, 0x80000000) ==/!= 0 ==> x >=/< 0.
Use bit information to improve Cmp optimization.
IA-32: Do not create cltd in case of only one user.

Using a sarl instruction has lower register demand.