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/JSystem/JSupport/JSUOutputStream.h

@@ -18,30 +18,24 @@ public:
     s32 write(const void*, s32);
 	void write(const char*);
 
-	JSUOutputStream& operator<<(u32 param_0) {
-        write(&param_0, sizeof(u32));
-        return *this;
+#define JSU_OUTPUTSTREAM_OPERATOR(T) \
+    JSUOutputStream& operator<<(T val) { \
+        write(&val, sizeof(T)); \
+        return *this; \
     }
 
-    JSUOutputStream& operator<<(s32 param_0) {
-        write(&param_0, sizeof(s32));
-        return *this;
-    }
+    JSU_OUTPUTSTREAM_OPERATOR(signed char)
+    JSU_OUTPUTSTREAM_OPERATOR(unsigned char)
+    JSU_OUTPUTSTREAM_OPERATOR(signed short)
+    JSU_OUTPUTSTREAM_OPERATOR(unsigned short)
+    JSU_OUTPUTSTREAM_OPERATOR(int)
+    JSU_OUTPUTSTREAM_OPERATOR(unsigned int)
+    JSU_OUTPUTSTREAM_OPERATOR(signed long)
+    JSU_OUTPUTSTREAM_OPERATOR(unsigned long)
+    JSU_OUTPUTSTREAM_OPERATOR(signed long long)
+    JSU_OUTPUTSTREAM_OPERATOR(unsigned long long)
 
-    JSUOutputStream& operator<<(s16 param_0) {
-        write(&param_0, sizeof(s16));
-        return *this;
-    }
-
-    JSUOutputStream& operator<<(u16 param_0) {
-        write(&param_0, sizeof(u16));
-        return *this;
-    }
-
-    JSUOutputStream& operator<<(u8 param_0) {
-        write(&param_0, sizeof(u8));
-        return *this;
-    }
+#undef JSU_OUTPUTSTREAM_OPERATOR
 
     JSUOutputStream& operator<<(const char* param_0) {
         write(param_0);

include/JSystem/JSupport/JSupport.h

@@ -20,7 +20,7 @@ T* JSUConvertOffsetToPtr(const void* ptr, uintptr_t offset) {
 template <typename T>
 T* JSUConvertOffsetToPtr(const void* ptr, const void* offset) {
     T* ret;
-    if (offset == NULL) {
+    if (offset == 0) {
         ret = NULL;
     } else {
         ret = (T*)((intptr_t)ptr + (intptr_t)offset);