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_resorce.cpp

@@ -49,7 +49,7 @@ int dRes_info_c::set(char const* i_arcName, char const* i_path, u8 i_mountDirect
     JUT_ASSERT(120, strlen(i_arcName) <= NAME_MAX);
 #endif
 
-    if (*i_path != NULL) {
+    if (*i_path != '\0') {
         char path[40];
         snprintf(path, sizeof(path), "%s%s.arc", i_path, i_arcName);
         mDMCommand = mDoDvdThd_mountArchive_c::create(path, i_mountDirection, i_heap);