[PATCH] Remove __PTHREAD_MUTEX_HAVE_ELISION undefined warning

[Roland McGrath]

> On Wed, 26 Mar 2014, Adhemerval Zanella wrote:
> 
> > +#define __PTHREAD_MUTEX_HAVE_ELISION 0
> 
> I think the default file should have a comment explaining what the 
> semantics of the possible values for this macro (0, 1 and 2) are.

Absolutely.  This is a general rule for any sysdeps/generic or similar file
that sets the terms of what identifiers sysdeps variants are required to
define and what their definitions mean.