More GCC compatibility/warning fixes (#3118)

* Wrap >4-char literals in a MULTI_CHAR macro

Modern compilers do not support CW's non-standard behavior with
>4 char literals. We can, however, use a constexpr function to
compute the u64 values directly. This leaves <=4 char literals
unchanged.

* Replace non-pointer usages of NULL with 0

* Define NULL to nullptr on C++11 and above

* Fix more -Wpointer-arith and -Woverflow warnings

* Replace u32/s32 with uintptr_t/intptr_t where appropriate

* JSUOutputStream: Overload all standard int types

src/d/actor/d_a_npc_kn.cpp

@@ -4965,7 +4965,7 @@ int daNpc_Kn_c::setPrtcl() {
                                                   mParticleMngr[i].mpModel == true ? &mParticleMngr[i].mAngle : NULL,
                                                   0, fopAcM_GetRoomNo(this), 0.0f, speedF);
 
-        if (mParticleMngr[i].mpModel != NULL) {
+        if (mParticleMngr[i].mpModel != false) {
             emitter = mParticleMngr[i].mManager.getCenterEmitter(0, 0);
             if (emitter != NULL) {
                 switch (i) {