Really fix posix includes (from Samuel Thibault)
<youpi> E* macros are reserved names in posix applications are not supposed to define
 them, actually
<youpi> well, strictly speaking, E[0-9A-Z].* are reserved so E_SUCCESS is fine.
"Additional macro definitions, beginning with E and a digit or E and an uppercase letter may also be specied by the implementation."
Merge pull request #594 from LocutusOfBorg/hurd-fix

Really fix posix includes (from Samuel Thibault)