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/m_Do/m_Do_ext.cpp

@@ -3713,7 +3713,7 @@ J3DModel* mDoExt_J3DModel__create(J3DModelData* i_modelData, u32 i_modelFlag, u3
             bool hasSharedDlistObj =
                 i_modelData->getMaterialNodePointer(0)->getSharedDisplayListObj() != NULL;
             // Update the modelFlag if the model data passed in has a shared dlist object
-            if (hasSharedDlistObj != NULL) {
+            if (hasSharedDlistObj != false) {
                 if (i_modelData->isLocked()) {
                     i_modelFlag = J3DMdlFlag_UseSharedDL;
                 } else if (i_modelFlag == J3DMdlFlag_UseSharedDL) {