cmd/compile/internal/ssagen: use an alias for math/bits.OnesCount
Currently, only amd64 has an intrinsic for math/bits.OnesCount, which
generates the same code as math/bits.OnesCount64. Replace this with
an alias that maps math/bits.OnesCount to math/bits.OnesCount64 on
64 bit platforms.
Change-Id: Ifa12a2173a201aacd52c3c22b9a948be6e314405
Reviewed-on: https://go-review.googlesource.com/c/go/+/659215 Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
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