dashboard: set GO{,HOST}ARCH, GOARM on linux-arm-aws builder

This change modifies the environmental variables for the linux-arm-aws
builder. It standardizes the environment that the linux/arm is tested
and released on.

Fixes golang/go#47554

Change-Id: Ie96ad93be20434636f29ab9c778fbed12fdb8d82
Reviewed-on: https://go-review.googlesource.com/c/build/+/340112
Trust: Carlos Amedee <carlos@golang.org>
Run-TryBot: Carlos Amedee <carlos@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index f945910..0a78c9a 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -2465,6 +2465,11 @@
 		HostType:          "host-linux-arm-aws",
 		tryBot:            defaultTrySet(),
 		numTryTestHelpers: 1,
+		env: []string{
+			"GOARCH=arm",
+			"GOARM=6",
+			"GOHOSTARCH=arm",
+		},
 	})
 	addBuilder(BuildConfig{
 		FlakyNet:       true,