Introduce MetaAddress

`MetaAddress` replaces all the `uint64_t` used to represent a virtual
address. Its main features are:

* It has a non-zero representation of invalid addresses.
* It supports tags to represent code that has different interpretations but
  resides at the same address in memory (namely ARM vs Thumb).
* Arithmetic operations cannot overflow.
* It supports epochs, a way we intend to employ to handle self-modifying code
  (i.e., different code at the same address at different times).
* It supports "address spaces", which enable handling architectures with
  multiple address spaces.
* It fits in two 64-bit registers.

lib/BasicAnalyses/GeneratedCodeBasicInfo.cpp

@@ -26,6 +26,10 @@ static RegisterGCBI X("gcbi", "Generated Code Basic Info", true, true);
 
 bool GeneratedCodeBasicInfo::runOnModule(llvm::Module &M) {
   Function &F = *M.getFunction("root");
+  NewPC = M.getFunction("newpc");
+  if (NewPC != nullptr) {
+    MetaAddressStruct = cast<StructType>(NewPC->arg_begin()->getType());
+  }
 
   revng_log(PassesLog, "Starting GeneratedCodeBasicInfo");
 
@@ -83,7 +87,7 @@ bool GeneratedCodeBasicInfo::runOnModule(llvm::Module &M) {
       case BlockType::JumpTargetBlock: {
         auto *Call = cast<CallInst>(&*BB.begin());
         revng_assert(Call->getCalledFunction()->getName() == "newpc");
-        JumpTargets[getLimitedValue(Call->getArgOperand(0))] = &BB;
+        JumpTargets[MetaAddress::fromConstant(Call->getArgOperand(0))] = &BB;
         break;
       }
       case BlockType::EntryPoint: