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/actor/d_a_e_df.cpp

@@ -659,7 +659,7 @@ int daE_DF_c::Create() {
             return cPhs_ERROR_e;
         }
 
-        if (fopAcM_entrySolidHeap(this, useHeapInit, 0x1a40) == NULL) {
+        if (fopAcM_entrySolidHeap(this, useHeapInit, 0x1a40) == false) {
             return cPhs_ERROR_e;
         }