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/JStudio/JStudio/fvb-data.h

@@ -14,7 +14,7 @@ extern const char ga4cSignature[4];
 
 const int PARAGRAPH_DATA = 1;
 
-typedef enum TEComposite {
+enum TEComposite {
     /* 0x0 */ COMPOSITE_NONE,
     /* 0x1 */ COMPOSITE_RAW,
     /* 0x2 */ COMPOSITE_IDX,

include/JSystem/JStudio/JStudio/stb.h

@@ -5,6 +5,7 @@
 #include "JSystem/JStudio/JStudio/object-id.h"
 #include "JSystem/JStudio/JStudio/stb-data-parse.h"
 #include <dolphin/os.h>
+#include <cstdint>
 
 namespace JStudio {
 class TObject;
@@ -86,7 +87,7 @@ public:
     const void* getSequence() const { return pSequence; }
     void setSequence_(const void* arg1) { pSequence = arg1; }
     const void* getSequence_offset(s32 i_no) const {
-        int s32Val = (s32)getSequence();
+        intptr_t s32Val = (intptr_t)getSequence();
         return (const void*)(s32Val + i_no);
     }
     const void* getSequence_next() const { return pSequence_next; }