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

include/dolphin/types.h

@@ -69,8 +69,12 @@ typedef unsigned int uint;
 #endif
 
 #ifndef NULL
-#ifdef  __cplusplus
+#ifdef __cplusplus
+#if __cplusplus >= 201103L
+#define NULL nullptr
+#else
 #define NULL 0
+#endif
 #else
 #define NULL ((void*)0)
 #endif