Use strtoll() for hex literals to handle 64-bit ones even on 32-bit.

test/language/number/hex_literals.wren

@@ -5,4 +5,5 @@ System.print(x + 1) // expect: 256
 System.print(x == 255) // expect: true
 System.print(0x09 is Num) // expect: true
 System.print(x is Num) // expect: true
-System.print(-0xFF) // expect: -255
+System.print(-0xFF) // expect: -255
+System.print(0xdeadbeef) // expect: 3735928559