cmd/dist: detect gohostarch for openbsd/mips64

On OpenBSD/octeon `uname -m` returns 'octeon' and we need `uname -p` to determine
the processor type (mips64).

Update #40995

Change-Id: I37c53ca2c372ab958fff17917d82d41f4b0a0393
Reviewed-on: https://go-review.googlesource.com/c/go/+/250583
Trust: Joel Sing <joel@sing.id.au>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/cmd/dist/main.go b/src/cmd/dist/main.go
index 37fc522..37de1ac 100644
--- a/src/cmd/dist/main.go
+++ b/src/cmd/dist/main.go
@@ -133,6 +133,10 @@
 			if strings.Contains(run("", CheckExit, "uname", "-v"), "RELEASE_ARM64_") {
 				gohostarch = "arm64"
 			}
+		case gohostos == "openbsd":
+			if strings.Contains(run("", CheckExit, "uname", "-p"), "mips64") {
+				gohostarch = "mips64"
+			}
 		default:
 			fatalf("unknown architecture: %s", out)
 		}