Introduce using to increase readibility

This commit introduces `using` statements and `constexpr` functions to
increase readibility of various types.

lib/StackAnalysis/stackanalysis.cpp

@@ -26,6 +26,7 @@
 using llvm::BasicBlock;
 using llvm::Function;
 using llvm::Module;
+using llvm::RegisterPass;
 
 namespace StackAnalysis {