- adds several config-options to allow for turning off certain features

- adds several config-options to allow for turning off certain features
  like
  o UCLIBC_HAS_GNU_ERROR
  o UCLIBC_HAS_BSD_ERR
  o UCLIBC_HAS_PTY
  o UCLIBC_HAS_GETPT (1)
  o UCLIBC_SYSCALL_STUBS
  o UCLIBC_SYSCALL_STUB_WARNING
  o UCLIBC_LINUX_SPECIFIC (2)
  o UCLIBC_BSD_SPECIFIC (3)
  o UCLIBC_NTP_LEGACY (4)
  o UCLIBC_SV4_DEPRECATED (5)
  o UCLIBC_HAVE_REALTIME (6)
  o UCLIBC_HAVE_ADVANCED_REALTIME (7)
  o UCLIBC_HAVE_EPOLL (8)
  o UCLIBC_HAVE_XATTR (9)
  o UCLIBC_HAVE_PROFILING (10)

(1) make non-standard getpt optional and implement standard posix_openpt
(2) fstatfs(), inotify_*(), ioperm(), iopl(), madvise(), modify_ldt(),
    personality()
    ppoll(), setresuid()
(3) mincore(), getdomainname(), setdomainname()
(4) ntp_adjtime(), ntp_gettime() aliases
(5) ustat() [use statfs(2) in your code instead]
(6) All marked as "(REALTIME)" in SUSv3
(7) All marked as "(ADVANCED REALTIME)" in SUSv3
(8) epoll_create(), epoll_ctl(), epoll_wait()
(9) all Extended Attributes
(10) helpers for gcc's -finstrument-functions

- Fixes _dl_exit()
- Implements sleep(3) for !UCLIBC_HAVE_REALTIME
- Implements usleep(3) for !UCLIBC_HAVE_REALTIME
- adds #warning about incorrect posix_fadvise{,64}()
- removes unused and unwanted uselib()

Net outcome is that an allnoconfig with HAVE_SHARED is now about 88k instead
of formerly 130k.