[lab3] add middle-end and backend with bugs to fix

src/SysYIRGenerator.cpp

@@ -12,7 +12,7 @@ std::string SysYIRGenerator::generateIR(SysYParser::CompUnitContext* unit) {
 }
 
 std::string SysYIRGenerator::getNextTemp() {
-    std::string ret = "%" + std::to_string(tempCounter++);
+    std::string ret = "%." + std::to_string(tempCounter++);
     tmpTable[ret] = "void";
     return ret;
 }