go: makes it build for the case $GOROOT has whitespaces

go: makes it build for the case $GOROOT has whitespaces

the bash scripts and makefiles for building go didn't take into account
the fact $GOROOT / $GOBIN could both be directories containing whitespaces,
and was not possible to build it in such a situation.

this commit adjusts the various makefiles/scripts to make it aware of that
possibility, and now it builds successfully when using a path with whitespaces
as well.

Fixes #115.

R=rsc, dsymonds1
https://golang.org/cl/157067