dashboard: set HostArch for host-solaris-oracle-amd64-oraclerel

Without an explicit HostArch set, this host name leads to "oracle"
being inferred as the GOARCH value, while in reality it is "amd64".

For golang/go#44505.

Change-Id: If3df135d75fae36d9f2fd55ef7f3ba140ecb609f
Reviewed-on: https://go-review.googlesource.com/c/build/+/421456
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 65586e9..f456028 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -475,6 +475,7 @@
 	},
 	"host-solaris-oracle-amd64-oraclerel": {
 		Notes:     "Oracle Solaris amd64 Release System",
+		HostArch:  "solaris-amd64",
 		Owners:    []*gophers.Person{gh("rorth")}, // https://github.com/golang/go/issues/15581#issuecomment-550368581
 		IsReverse: true,
 		ExpectNum: 1,