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_cc_d.cpp

@@ -255,7 +255,7 @@ dCcD_GObjInf* dCcD_GObjInf::GetTgHitGObj() {
 u8 dCcD_GObjInf::GetTgHitObjSe() {
     dCcD_GObjInf* objInf = GetTgHitGObj();
     if (objInf == NULL) {
-        return NULL;
+        return 0;
     } else {
         return objInf->GetAtSe();
     }