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_rafrel.cpp

@@ -421,7 +421,7 @@ int daNpcRafrel_c::createHeapCallBack(fopAc_ac_c* i_this) {
 }
 
 int daNpcRafrel_c::ctrlJointCallBack(J3DJoint* i_joint, int param_1) {
-    if (param_1 == NULL) {
+    if (param_1 == 0) {
         J3DModel* mdl_p = j3dSys.getModel();
         daNpcRafrel_c* i_this = (daNpcRafrel_c*)mdl_p->getUserArea();