[U]

[..]
  1. U32T
  2. U64T
  3. U64TS
  4. UNALIGNED_P
  5. UNPROMOTED_INSTANCES
  6. UPSTART_06_API
  7. UPSTART_JOB_IFACE
  8. UPSTART__H
  9. USE_GNU
  10. US_AUTH_PEERCRED_UCRED
[..]