This, at present, is overly simplistic and makes many stupid assumptions:

• That the return type is short.
• That there are no short global variables declared.
• That everything is well-formatted so that the return type is always first column, and that there is a space between both function name and return type (as in, only spaces–no comments) and function name and open parenthesis of the arg list.

cat $1 | awk '
BEGIN {
    functionNameFile="";
}
/^short/ {
    /* assumes return type of short */
    /* assumes space between return type, function name, and parm list */
    functionNameFile=$2.".c";
    print $0 > functionNameFile;
}
/^}/ {
    print $0 >> functionNameFile;
    functionNameFile="";
    next;
}
{
    if(functionNameFile    != "") {
        print $0 >> functionNameFile;
    }
}
'