Depends on CL 6197045.

Result obtained on Core i7 620M, Darwin/amd64:
benchmark                       old ns/op    new ns/op    delta
BenchmarkComplex128DivNormal           57           28  -50.78%
BenchmarkComplex128DivNisNaN           49           15  -68.90%
BenchmarkComplex128DivDisNaN           49           15  -67.88%
BenchmarkComplex128DivNisInf           40           12  -68.50%
BenchmarkComplex128DivDisInf           33           13  -61.06%

Result obtained on Core i7 620M, Darwin/386:
benchmark                       old ns/op    new ns/op    delta
BenchmarkComplex128DivNormal           89           50  -44.05%
BenchmarkComplex128DivNisNaN          307          802  +161.24%
BenchmarkComplex128DivDisNaN          309          788  +155.02%
BenchmarkComplex128DivNisInf          278          237  -14.75%
BenchmarkComplex128DivDisInf           46           22  -52.46%

Result obtained on 700MHz OMAP4460, Linux/ARM:
benchmark                       old ns/op    new ns/op    delta
BenchmarkComplex128DivNormal         1557          465  -70.13%
BenchmarkComplex128DivNisNaN         1443          220  -84.75%
BenchmarkComplex128DivDisNaN         1481          218  -85.28%
BenchmarkComplex128DivNisInf          952          216  -77.31%
BenchmarkComplex128DivDisInf          861          231  -73.17%

The 386 version has a performance regression, but as we have
decided to use SSE2 instead of x87 FPU for 386 too (issue 3912),
I won't address this issue.

R=dsymonds, mchaten, iant, dave, mtj, rsc, r
CC=golang-dev
https://golang.org/cl/6024045