Implement mman.h definitions

Implement the sys/mman.h definitions.

• options

  • PROT_READ
  • PROT_WRITE
  • PROT_EXEC
  • PROT_NONE

• flags

  • MAP_SHARED
  • MAP_PRIVATE
  • MAP_FAILED (implemented in bits/sys/mman.h)

• mlock and posix_madvise constants

• more