$ goinstall launchpad.net/gommap
/bin/bash: === cd /usr/local/Cellar/go/r60.3/src/pkg/launchpad.net/gommap; bash gomake -f- install
6g -I "/usr/local/Cellar/go/r60.3/pkg/darwin_amd64"  -o _go_.6 consts.go gommap.go
gommap.go:59: undefined: mmap_syscall
make: *** [_go_.6] Error 1
--- exit status 2
goinstall: launchpad.net/gommap: install: running bash: exit status 2 ($GOPATH not set)