[RFC] Faster strspn/strcspn implementation.

[Joseph S. Myers]

On Fri, 28 Dec 2012, Paul Eggert wrote:

> So there is some precedent for glibc using
> str[a-z]* symbols that are not formally standardized.

In this case, however, string.h only declares strchrnul if _GNU_SOURCE, 
meaning use in a macro definition of a function that is declared in some 
other case (POSIX.1-2008) is inappropriate.

-- 
Joseph S. Myers
joseph@codesourcery.com