Prevent generateASTNode from overwriting a file if it already exists

tools/generateASTNode.sh

@@ -5,6 +5,14 @@ if [ "$1" == "" ]; then
 exit 1
 fi
 
+if [ -f $1.cpp ]; then
+exit 0
+fi
+
+if [ -f $1.h ]; then
+exit 0
+fi
+
 touch $1.cpp
 touch $1.h
 
@@ -39,4 +47,4 @@ llvm::Value* $1::codegen(IRBuilder* generator)
     return llvm::ConstantInt::getSigned(llvm::IntegerType::getInt32Ty(generator->getBuilder()->getContext()),
                                                 0);
 }
-EOF
+EOF