tcg/optimize: optimize TSTNE using smask and zmask

tcg/optimize: optimize TSTNE using smask and zmask

Generalize the existing optimization of "TSTNE x,sign" and "TSTNE x,-1".
This can be useful for example in the i386 frontend, which will generate
tests of zero-extended registers against 0xffffffff.

Ironically, on x86 hosts this is a very slight pessimization in the very
case it's meant to optimize because

 brcond_i64 cc_dst,$0xffffffff,tsteq,$L1

(test %ebx, %ebx) is 1 byte smaller than

 brcond_i64 cc_dst,$0x0,eq,$L1

(test %rbx, %rbx).  However, in general it is an improvement, especially
if it avoids placing a large immediate in the constant pool.

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