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://codereview.appspot.com/82030043

karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,chenjianlong/go.tools,chenjianlong/go.tools,chenjianlong/go.tools,karmakaze/go.tools