Merge remote-tracking branch 'aosp/upstream' into master

* aosp/upstream:
  Workaround gimme not setting GOROOT
  Export GOROOT for minibp / primary builder
  Support parallel Go compiles with Go 1.9
  Fix build on Go 1.9

Test: m -j nothing with Go 1.8
Test: m -j nothing with Go 1.9rc1
Change-Id: Ib47750adc88728be8c1f3e8d27364ed652204d82