[lcheylus]

Check if a child process could trace its parent process, if not a debugger must be present.

On OpenBSD, impossible to trace a parent process from its child. But with errors (errno), it's possible to determine if a debugger is present or not.
Possible errors for ptrace / PT_ATTACH in child process:

• EBUSY: process already traced
• EPERM: process is not a child of tracer (sysctl kern.global_ptrace=0)
• EINVAL: process is an ancestor of the current process and not init (sysctl kern.global_ptrace=1)

Closes #23603

---

Tests OK on OpenBSD current/adm64

Code debugger_present.v to test if debugger is present or not

import os

fn main() {
        println('Call 1:')
        if os.debugger_present() {
                println('debugger here')
        } else {
                println('no debugger')
        }

        println('Call 2:')
        if os.debugger_present() {
                println('debugger here')
        } else {
                println('no debugger')
        }
}

• Tests WITHOUT debugger:

$ ~/tmp/debugger_present
Call 1:
no debugger
Call 2:
no debugger

• Test WITH debugger (gdb)

$ gdb ~/tmp/debugger_present
(...)
(gdb) run
Starting program: /home/fox/tmp/debugger_present 
Call 1:
[New process 84238]
debugger here
Call 2:
debugger here

Program exited normally.
(gdb) quit

[huly-for-github]

Connected to Huly®: V_0.6-22859

[spytheman]

Excellent work.