cmd/dist, internal/platform: mark freebsd/riscv64 broken

It seems we have a builder, but it is not running correctly. Until
then, we should mark this port broken.

For #74734
For #74735

Change-Id: I536d037a43499cbd033fb6ebdf004a3df76332ab
Reviewed-on: https://go-review.googlesource.com/c/go/+/691835
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: Mark Freeman

src/cmd/dist/build.go

@@ -1828,9 +1828,10 @@ var cgoEnabled = map[string]bool{
 // get filtered out of cgoEnabled for 'dist list'.
 // See go.dev/issue/56679.
 var broken = map[string]bool{
-	"linux/sparc64":  true, // An incomplete port. See CL 132155.
-	"openbsd/mips64": true, // Broken: go.dev/issue/58110.
-	"windows/arm":    true, // Broken: go.dev/issue/68552.
+	"freebsd/riscv64": true, // Broken: go.dev/issue/73568.
+	"linux/sparc64":   true, // An incomplete port. See CL 132155.
+	"openbsd/mips64":  true, // Broken: go.dev/issue/58110.
+	"windows/arm":     true, // Broken: go.dev/issue/68552.
 }
 
 // List of platforms which are first class ports. See go.dev/issue/38874.