Switch to PPSSPP's assert functions (don't use the system's)

Core/HLE/sceKernelThread.cpp

@@ -1529,7 +1529,7 @@ void __KernelWaitCurThread(WaitType type, SceUID waitID, u32 waitValue, u32 time
 	}
 
 	PSPThread *thread = __GetCurrentThread();
-	assert(thread != nullptr);
+	_assert_(thread != nullptr);
 	thread->nt.waitID = waitID;
 	thread->nt.waitType = type;
 	__KernelChangeThreadState(thread, ThreadStatus(THREADSTATUS_WAIT | (thread->nt.status & THREADSTATUS_SUSPEND)));