[Bug c/33167] Hex constant characters with \x escape not parsing correctly

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=33167

--- Comment #7 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
"longest sequence of characters that can constitute the escape sequence" 
resolves an ambiguity between alternative parses permitted by the syntax; 
it doesn't need to deal with anything that is not permitted by the syntax.  
Four or more octal characters in an octal sequence are not a parse 
permitted by the syntax, whereas more than two hex characters in a hex 
sequence are a parse permitted by the syntax.