math: use Abs in Mod rather than if x < 0 { x = -x}
math: use Abs in Mod rather than if x < 0 { x = -x}

goos: linux
goarch: amd64
pkg: math

name  old time/op  new time/op  delta
Mod   64.7ns ± 2%  63.7ns ± 2%  -1.52%  (p=0.003 n=8+10)

Change-Id: I851bec0fd6c223dab73e4a680b7393d49e81a0e8
Reviewed-on: https://go-review.googlesource.com/c/85095
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

cloudflare/go,akutz/go,cloudflare/go,CAFxX/go,nawawi/go,golang/go,golang/go,nawawi/go,cloudflare/go,akutz/go,golang/go,golang/go,josharian/go,golang/go,cloudflare/go,akutz/go,josharian/go,golang/go,golang/go,CAFxX/go,CAFxX/go,akutz/go,nawawi/go,nawawi/go,nawawi/go,akutz/go,cloudflare/go,akutz/go,josharian/go,nawawi/go,CAFxX/go,cloudflare/go,nawawi/go,akutz/go,josharian/go,golang/go,josharian/go,josharian/go,CAFxX/go,nawawi/go,CAFxX/go,cloudflare/go,josharian/go,josharian/go,akutz/go,CAFxX/go,cloudflare/go,CAFxX/go