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

include/JSystem/J2DGraph/J2DAnimation.h

@@ -59,7 +59,7 @@ public:
     J2DAnmVtxColor() {
         mKind = KIND_VTX_COLOR;
         for (int i = 0; i < ARRAY_SIZE(mAnmTableNum); i++) {
-            mAnmTableNum[i] = NULL;
+            mAnmTableNum[i] = 0;
         }
         for (int i = 0; i < ARRAY_SIZE(mVtxColorIndexData); i++) {
             mVtxColorIndexData[i] = NULL;