That will be the go version at compile time. So read $GOROOT/VERSION, or
fall back to executing `$GOROOT/bin/go version` to find the go version
currently in GOROOT.
Test: Ensure everything rebuilds when switching between go1.8rc2 and go1.8
Change-Id: I8738a7aa249a088b1e0668af260fa3974844dab7
microfactory is a tool to incrementally compile a go program. It's
similar to `go install`, but doesn't require a GOPATH. A package->path
mapping can be specified as command line options. All input files are
hashed, and if any change, the necessary packages will be rebuilt.
microfactory can (re)build itself as necessary, so combined with a shell
script that runs `go run microfactory.go` the first time, it can
bootstrap a go program entirely from sources with just a working goroot.
Time to build soong_ui only using source & GOROOT:
first time no-change incremental
microfactory 1400ms 15ms
go install 670ms 130ms
While microfactory takes longer the first time, almost half of that time
is from `go run` and building microfactory for use later. If
microfactory only has to build soong_ui, it's about 580ms.
Test: USE_SOONG_UI=true m -j blueprint_tools
Test: go test -bench . build/soong/cmd/microfactory/microfactory_test.go
Change-Id: I4d2b9825788144fa10042bbd804482e44f459a54
