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_shad.cpp

@@ -1485,7 +1485,7 @@ bool daNpcShad_c::talk(void* param_1) {
             if (strcmp(dComIfGp_getStartStageName(), "R_SP116") == 0 || mCurAngle.y == fopAcM_searchPlayerAngleY(this)) {
                 if (talkProc(NULL, TRUE, NULL)) {
                     mActorMngr[0].entry(daPy_getPlayerActorClass());
-                    itemNo = NULL;
+                    itemNo = 0;
                     eventID = mFlow.getEventId(&itemNo);
                     OS_REPORT("会話終了時 イベントID=%d アイテムNo=%d\n", eventID, itemNo); // At the end of the conversation, Event ID=%d Item No=%d