stage0: add support for MIPS builders to stage0

Updates golang/go#31217

Change-Id: Icf328cb39086fa4196940345c35969a8b26eafb0
Reviewed-on: https://go-review.googlesource.com/c/build/+/205797
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/cmd/buildlet/stage0/Makefile b/cmd/buildlet/stage0/Makefile
index 2361d1b..db65729 100644
--- a/cmd/buildlet/stage0/Makefile
+++ b/cmd/buildlet/stage0/Makefile
@@ -50,10 +50,22 @@
 	go install golang.org/x/build/cmd/upload
 	upload --verbose --osarch=$@ --file=go:golang.org/x/build/cmd/buildlet/stage0 --public --cacheable=false go-builder-data/$@
 
+buildlet-stage0.linux-mipsle: FORCE
+	go install golang.org/x/build/cmd/upload
+	upload --verbose --osarch=$@ --file=go:golang.org/x/build/cmd/buildlet/stage0 --public --cacheable=false go-builder-data/$@
+
 buildlet-stage0.linux-mips64le: FORCE
 	go install golang.org/x/build/cmd/upload
 	upload --verbose --osarch=$@ --file=go:golang.org/x/build/cmd/buildlet/stage0 --public --cacheable=false go-builder-data/$@
 
+buildlet-stage0.linux-mips: FORCE
+	go install golang.org/x/build/cmd/upload
+	upload --verbose --osarch=$@ --file=go:golang.org/x/build/cmd/buildlet/stage0 --public --cacheable=false go-builder-data/$@
+
+buildlet-stage0.linux-mips64: FORCE
+	go install golang.org/x/build/cmd/upload
+	upload --verbose --osarch=$@ --file=go:golang.org/x/build/cmd/buildlet/stage0 --public --cacheable=false go-builder-data/$@
+
 # macstadium uploads all the darwin-amd64 stage0 binary as three
 # different filenames, which is used by four different Mac VM images.
 # See the env/darwin/macstadium/** files for details.
diff --git a/cmd/buildlet/stage0/stage0.go b/cmd/buildlet/stage0/stage0.go
index 5030f19..23d4b63 100644
--- a/cmd/buildlet/stage0/stage0.go
+++ b/cmd/buildlet/stage0/stage0.go
@@ -163,6 +163,14 @@
 	case "host-linux-mipsle-mengzhuo":
 		cmd.Args = append(cmd.Args, reverseHostTypeArgs(buildEnv)...)
 		cmd.Args = append(cmd.Args, os.ExpandEnv("--workdir=${WORKDIR}"))
+	case "host-linux-mips64le-rtrk":
+		cmd.Args = append(cmd.Args, reverseHostTypeArgs(buildEnv)...)
+		cmd.Args = append(cmd.Args, os.ExpandEnv("--workdir=${WORKDIR}"))
+		cmd.Args = append(cmd.Args, os.ExpandEnv("--hostname=${GO_BUILDER_ENV}"))
+	case "host-linux-mips64-rtrk":
+		cmd.Args = append(cmd.Args, reverseHostTypeArgs(buildEnv)...)
+		cmd.Args = append(cmd.Args, os.ExpandEnv("--workdir=${WORKDIR}"))
+		cmd.Args = append(cmd.Args, os.ExpandEnv("--hostname=${GO_BUILDER_ENV}"))
 	case "host-linux-ppc64le-power9-osu":
 		cmd.Args = append(cmd.Args, reverseHostTypeArgs(buildEnv)...)
 	case "host-linux-ppc64le-osu": // power8
@@ -308,8 +316,14 @@
 		return "https://storage.googleapis.com/go-builder-data/buildlet.linux-ppc64"
 	case "linux/ppc64le":
 		return "https://storage.googleapis.com/go-builder-data/buildlet.linux-ppc64le"
+	case "linux/mipsle":
+		return "https://storage.googleapis.com/go-builder-data/buildlet.linux-mipsle"
 	case "linux/mips64le":
 		return "https://storage.googleapis.com/go-builder-data/buildlet.linux-mips64le"
+	case "linux/mips":
+		return "https://storage.googleapis.com/go-builder-data/buildlet.linux-mips"
+	case "linux/mips64":
+		return "https://storage.googleapis.com/go-builder-data/buildlet.linux-mips64"
 	case "solaris/amd64":
 		return "https://storage.googleapis.com/go-builder-data/buildlet.solaris-amd64"
 	case "illumos/amd64":