c语言代码，实现在一字符串中查询子字符串，如果找到，返回子字符串位置
Write the following function in C.
stripos — Find position of first occurrence of a case-insensitive string
int stripos ( char* haystack, char* needle, int offset )
Returns the numeric position of the first occurrence of needle in the haystack string. Note that the needle may be a string of one or more characters. If needle is not found, stripos() will return -1.
