#C 59 Bytes

r;f(s)char*s;{for(r=0;r=*s?~r&1<<(*s>=*++s):0;);return!*s;}

C 59 Bytes

r;f(s)char*s;{for(r=0;r=*s?~r&1<<(*s>=*++s):0;);return!*s;}

#C 57 Bytes

f(r,s)char*s;{for(;r=*s?~r&1<<(*s>=*++s):0;);return !*s;}

#C 59 Bytes

r;f(s)char*s;{for(r=0;r=*s?~r&1<<(*s>=*++s):0;);return!*s;}

#C 133 125 118 116 106 102 89 88 81 70 58 55 Bytes

r;f(char*s){for(;r=*s?~r&1<<(*s>=*++s):0;);return !*s;}

in case you can't set r=0 before calling the function for a second time it's 58 Bytes

r;f(char*s){for(r=0;r=*s?~r&1<<(*s>=*++s):0;);return !*s;}

Test it with this main function

main(c,v)char**v;
{
    f(v[1])?puts("T"):puts("F");
}

#C 57 Bytes

f(r,s)char*s;{for(;r=*s?~r&1<<(*s>=*++s):0;);return !*s;}