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_s_play.cpp

@@ -554,7 +554,7 @@ static int phase_3(dScnPly_c* i_this) {
         return cPhs_INIT_e;
     }
 
-    if (!i_this->field_0x1d0 == NULL && !i_this->field_0x1d0->sync()) {
+    if (i_this->field_0x1d0 != NULL && !i_this->field_0x1d0->sync()) {
         return cPhs_INIT_e;
     }