fix(freeze): Add include

Author: misonijnik

Diff for: lib/Module/FreezeLower.cpp

@@ -10,6 +10,7 @@
 #include "Passes.h"
 
 #include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constant.h"
 #include "llvm/IR/Instruction.h"
 
 namespace klee {