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_bg_w_kcol.cpp

@@ -689,9 +689,9 @@ void dBgWKCol::ShdwDraw(cBgS_ShdwDraw* param_0) {
 
                     do {
                         stepY_sp78 = 1000000;
-                        best1_sp70 = NULL;
-                        best2_sp6C = NULL;
-                        best3_sp68 = NULL;
+                        best1_sp70 = 0;
+                        best2_sp6C = 0;
+                        best3_sp68 = 0;
 
                         int x_sp44 = minX_spA0;
                         do {