cmd/dist: mark cgo as disabled on linux/riscv64

cgo is not currently supported on this platform.

Updates #27532 and #36641

Change-Id: I4b35f887e869ebc5c156dd754b1c79897a8c5800
Reviewed-on: https://go-review.googlesource.com/c/go/+/215838
Reviewed-by: Cherry Zhang <[email protected]>

Author: 4a6f656c

Diff for: src/cmd/dist/build.go

@@ -1532,7 +1532,7 @@ var cgoEnabled = map[string]bool{
 	"linux/mipsle":    true,
 	"linux/mips64":    true,
 	"linux/mips64le":  true,
-	"linux/riscv64":   true,
+	"linux/riscv64":   false, // Issue 36641
 	"linux/s390x":     true,
 	"linux/sparc64":   true,
 	"android/386":     true,