x/crypto/chacha20poly1305: needs +build go1.7 tags

[bradfitz]

The new chacha20poly1305 package needs +build go1.7 build tags apparently. It's failing on Go 1.6:

# golang.org/x/crypto/chacha20poly1305
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:780: unrecognized instruction "VPADDD"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:795: unrecognized instruction "VPADDD"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:796: unrecognized instruction "VPALIGNR"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:797: unrecognized instruction "VPADDD"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:798: unrecognized instruction "VPALIGNR"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:802: unrecognized instruction "VPADDD"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:803: unrecognized instruction "VPADDD"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:804: unrecognized instruction "VPADDD"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:805: unrecognized instruction "VPADDD"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:807: unrecognized instruction "VPERM2I128"
/var/folders/dx/k53rs1s93538b4x20g46cj_w0000gn/T/workdir/gopath/src/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s:814: unrecognized instruction "VPERM2I128"
asm: too many errors

[gopherbot]

CL https://golang.org/cl/30971 mentions this issue.

[gopherbot]

CL https://golang.org/cl/31492 mentions this issue.