[Bug target/36557] -m32 -mpowerpc64 produces better code than -m64 for a!=0

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36557

--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Still happens.  It now does

cntlzw 3,3
srwi 3,3,5
xori 3,3,0x1
rldicl 3,3,0,63
blr

which is better but not exactly ideal yet.