Kernel+LibELF: Store termination signal in coredump ProcessInfo

Author: https://github.com/linusg
Commit: 0571a17f57
Pull-request: https://github.com/SerenityOS/serenity/pull/4780

Kernel/Process.h

@@ -449,6 +449,8 @@ public:
     void terminate_due_to_signal(u8 signal);
     KResult send_signal(u8 signal, Process* sender);
 
+    u8 termination_signal() const { return m_termination_signal; }
+
     u16 thread_count() const
     {
         return m_thread_count.load(AK::MemoryOrder::memory_order_relaxed);