feat(debug): port the debugger to FreeBSD

Assisted-by: GLM 5.3 Flash

docs/CLI.md

@@ -287,7 +287,8 @@ Usage: gasm debug <file.s> --func <name>
 The debugger re-executes the binary it is running as (`os.Executable()`) for the
 traced child, so the child is the same `gasm`, whether it is installed on `$PATH`
 or run with `go run ./cmd/gasm`; nothing has to be installed first. Requires
-Linux (ptrace), and all four architectures are supported.
+Linux or FreeBSD (ptrace): all four architectures on Linux, amd64, arm64 and
+riscv64 on FreeBSD.
 
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