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/DynamicLink.cpp

@@ -224,7 +224,7 @@ bool DynamicModuleControl::do_load() {
                 mModule = (OSModuleHeader*)JKRDvdToMainRam(
                     buffer, NULL, EXPAND_SWITCH_UNKNOWN1, NULL, heap,
                     JKRDvdRipper::ALLOC_DIRECTION_FORWARD, 0, NULL, NULL);
-                if (mModule != NULL) {
+                if (mModule != 0) {
                     mSize = 0;
                     mResourceType = 7;
                 }