cmd/buildlet/stage0: add freebsd-riscv64-unmatched

For golang/go#53466

Change-Id: I7fac91b7d4d8e31f922f3e2342bd198c60dbf54a
Reviewed-on: https://go-review.googlesource.com/c/build/+/432656
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/cmd/buildlet/stage0/stage0.go b/cmd/buildlet/stage0/stage0.go
index 9fc79f0..9f162c0 100644
--- a/cmd/buildlet/stage0/stage0.go
+++ b/cmd/buildlet/stage0/stage0.go
@@ -172,6 +172,9 @@
 		cmd.Args = append(cmd.Args, reverseHostTypeArgs(buildEnv)...)
 	case "host-linux-amd64-wsl", "host-linux-riscv64-unmatched":
 		cmd.Args = append(cmd.Args, reverseHostTypeArgs(buildEnv)...)
+	case "host-freebsd-riscv64-unmatched":
+		cmd.Args = append(cmd.Args, reverseHostTypeArgs(buildEnv)...)
+		cmd.Args = append(cmd.Args, os.ExpandEnv("--workdir=${WORKDIR}"))
 	}
 	switch osArch {
 	case "linux/s390x":