[X86] ReplaceNodeResults - shrink i64 CTPOP to (shifted) CTPOP i32 if 32 or...

[X86] ReplaceNodeResults - shrink i64 CTPOP to (shifted) CTPOP i32 if 32 or less active bits to avoid SSE2 codegen

32-bit targets perform i64 CTPOP as a v2i64 CTPOP - if we can perform this as a i32 CTPOP by shifting the source bits, then do so to avoid the gpr<->xmm

This also triggers on non-SSE2 capable targets, as can be seen with the minor codegen diffs in ctpop_shifted_mask16