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_obj_avalanche.cpp

@@ -253,7 +253,7 @@ int daObjAvalanche_c::demoProc() {
 void daObjAvalanche_c::setEffect() {
     cXyz acStack_18(0.0f, 0.0f, 0.0f);
     csXyz cStack_20(0, 0, 0);
-    dComIfGp_particle_set(0x8c51, &acStack_18, &cStack_20, NULL, 0xff, NULL, 0xffffffff, NULL, NULL,
+    dComIfGp_particle_set(0x8c51, &acStack_18, &cStack_20, NULL, 0xff, NULL, -1, NULL, NULL,
                           NULL);
 }