Kernel: Rework all signal code

Signal handling code was way too complex. Now everything is
simplified and there is no need for ThreadBlockers.

Only complication that this patch includes is that blocking syscalls
have to manually be made interruptable by signal. There might be some
clever solution to combat this is make this happen automatically.

kernel/kernel/Process.cpp

@@ -257,7 +257,10 @@ namespace Kernel
 		LockGuard _(m_lock);
 		m_exit_status.exit_code = __WGENEXITCODE(status, signal);
 		for (auto* thread : m_threads)
-			thread->set_terminating();
+			if (thread != &Thread::current())
+				thread->terminate();
+		if (this == &Process::current())
+			Thread::current().terminate();
 	}
 
 	size_t Process::proc_meminfo(off_t offset, BAN::ByteSpan buffer) const
@@ -334,7 +337,7 @@ namespace Kernel
 	BAN::ErrorOr<long> Process::sys_exit(int status)
 	{
 		exit(status, 0);
-		Thread::TerminateBlocker _(Thread::current());
+		Thread::current().terminate();
 		ASSERT_NOT_REACHED();
 	}
 
@@ -1235,6 +1238,8 @@ namespace Kernel
 					{
 						CriticalScope _;
 						process.m_signal_pending_mask |= 1 << signal;
+						// FIXME: This is super hacky
+						Scheduler::get().unblock_thread(process.m_threads.front()->tid());
 					}
 					return (pid > 0) ? BAN::Iteration::Break : BAN::Iteration::Continue;
 				}