P.S: RFA: fix gcc.dg/tree-ssa/popcount4l.c 16 bit failure, improve 64 bit popcount expansion for 32 bit target

[Joern Wolfgang Rennecke]

Bootstrapped and regression tested in gcc version
d6f1cf644c45b76a27b6a6869dedaa030e3c7570 on x86_64 GNU/Linux .