x/build: plan9 arm builder failed

[cuonglm]

https://build.golang.org/log/b612441c65daaac63868cfa88ef392fd9f2fc815

go: not found
/boot/workdir/go/bin/go: '/boot/workdir/go/bin' does not exist
WARNING: /sys/lib/go1.16/bin/go does not exist, found /bin/go from env
rc (make.rc): null list in concatenation

build failed: make script failed: exit status: 'make.rc 183: error'

cc @golang/release

[dmitshur]

CC @0intro via builder owners.

There's a similarity to CL 354752. CC @bcmills.

It looks like it's been fixed recently (thank you!). The most recent plan9-arm build logs, such as https://build.golang.org/log/4b1a35038d21724217f2669393fbfa36bbe1fede, include:

"GOROOT_BOOTSTRAP=/boot/workdir/go1.4" [...] "GOROOT_BOOTSTRAP=/sys/lib/go1.17"
[...]
Building Go cmd/dist using /sys/lib/go1.17

So it looks like the builder was updated to use 1.17 as the bootstrap version (the duplicate "GOROOT_BOOTSTRAP=/boot/workdir/go1.4" environment entry is being shadowed by a later GOROOT_BOOTSTRAP entry).