Since ld.so internal mmap functions are only used internally in ld.so,
they can be made hidden. Don't hide __mmap on Hurd, since __mmap in
ld.so will be preempted by the one in libc.so after bootstrap.
[BZ #19122]
* include/sys/mman.h [IS_IN (rtld)]: Include <dl-mman.h>.
* sysdeps/generic/dl-mman.h: New file.
* sysdeps/mach/hurd/dl-mman.h: Likewise.