go.tools/cmd/godex: permit absolute paths for gccgo-generated package (export) files
go.tools/cmd/godex: permit absolute paths for gccgo-generated package (export) files

TBR=adonovan

TBR=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/82030043

maddyonline/tools,golang/tools,springning/tools,maddyonline/tools,sshetty10/tools,argandas/tools,josharian/tools,matryer/tools,golang/tools,josharian/tools,4ad/tools,nicot/tools,syreclabs/go-tools,jdhenke/tools,maddyonline/tools,runcom/tools,magiccao/tools,josharian/tools,magiccao/tools,runcom/tools,argandas/tools,cw2018/tools,cw2018/tools,magiccao/tools,argandas/tools,jdhenke/tools,syreclabs/go-tools,maddyonline/tools,glasser/golang-tools,springning/tools,josharian/tools,syreclabs/go-tools,dmitris/tools,cw2018/tools,glasser/golang-tools,argandas/tools,golang/tools,cmars/tools,jdhenke/tools,jdhenke/tools,magiccao/tools,runcom/tools,springning/tools,cmars/tools,cmars/tools,dmitris/tools,sshetty10/tools,syreclabs/go-tools,golang/tools,sshetty10/tools,sshetty10/tools,glasser/golang-tools,golang/tools,matryer/tools,nicot/tools,dmitris/tools,4ad/tools,runcom/tools,nicot/tools,springning/tools,cmars/tools,syreclabs/go-tools,matryer/tools,glasser/golang-tools,cw2018/tools,4ad/tools,nicot/tools,dmitris/tools,matryer/tools,syreclabs/go-tools