How To Disable Building getreent.c

[Joel Sherrill]

Hi

RTEMS is now providing its own version of __getreent() and
in some situations we are getting link errors because one
is in RTEMS and another is in the newlib libc.a.

The method in libc/getreent.c isn't wrapped by a conditional.
I assume adding something to configure.host and using that
to disable the contents of libc/getreent.c is the right
approach. Would GETREENT_PROVIDED be OK for the conditional?

There is already MALLOC_PROVIDED so this would at least
be consistent with one other host feature macro.

Thanks.

--joel