Write a function called merge_lists that takes two call-by-reference arguments that are pointer variables that point to the heads of linked lists of values of type int. The two linked lists are assumed to be sorted so that

the number at the head is the smallest number, the number in the next

node is the next smallest, and so forth. The function returns a pointer to

the head of a new linked list that contains all of the nodes in the original

two lists. The nodes in this longer list are also sorted from smallest to largest values. Note that your function will neither create nor destroy any

nodes. When the function call ends, the two pointer variable arguments

should have the value NULL