`svn update` would fail if the updated files were in the gcc/libgo or gcc/go/gofrontend because unrevisioned versions of those files had been inserted in the last build of gcc.
R=adg, adg
CC=golang-dev
https://golang.org/cl/14299043
Downloading the GCC repo takes a lot of time and everything works fine if we just store it in the buildRoot and reuse it.
R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/13583045
* Added --tool flag that allows user to specify "gccgo" as the tool to build.
* Added builderEnv struct to abstract away setting up the build.
* Made envv and envvWindows methods of the builderEnv struct.
* Modified Builder.envv() to wrap envv and envvWindows
* Added internal builderEnv in Builder.
R=adg
CC=golang-dev
https://golang.org/cl/13240044