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/d_s_room.cpp

@@ -326,7 +326,7 @@ static int phase_1(room_of_scene_class* i_this) {
         } else {
             stage_stag_info_class* stagInfo = dComIfGp_getStage()->getStagInfo();
 
-            if (dStage_staginfo_GetArchiveHeap(stagInfo) != NULL) {
+            if (dStage_staginfo_GetArchiveHeap(stagInfo) != FALSE) {
                 heap = mDoExt_getArchiveHeap();
             }
         }