poly1305/arm: allow building with Go 1.3
poly1305/arm: allow building with Go 1.3

This is the same as https://golang.org/cl/154120043

Since the file textflag.h is not available on Go 1.3, the macros defined
in textflag.h are replaced with their respective value.

Fixes golang/go#11448

Change-Id: I0d4aed67b7afe50d8e4e88915edd2cefeac4cc96
Reviewed-on: https://go-review.googlesource.com/12033
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

kim-racktop/crypto,bford/golang-x-crypto,cmars/tools,cmars/tools,lucevers/crypto,pki-io/crypto,golang/crypto,mattharden/crypto,tca/crypto,golang/crypto,ScriptRock/crypto,thomaso-mirodin/crypto,mattharden/crypto,cmars/tools,juniorz/crypto,CodyGuo/crypto,guaiguaihw/crypto,Carrotman42/crypto,lucevers/crypto,a-palchikov/crypto,CodyGuo/crypto,cmars/tools,golang/crypto,bford/golang-x-crypto,thomaso-mirodin/crypto,tca/crypto,a-palchikov/crypto,pki-io/crypto,Carrotman42/crypto,zj8487/crypto,zj8487/crypto,ScriptRock/crypto,juniorz/crypto,guaiguaihw/crypto,kim-racktop/crypto