* sysdeps/generic/dl-fcntl.h: New file, adds attribute_hidden to __open
and __fcntl.
* sysdeps/mach/hurd/dl-fcntl.h: New file, adds attribute_hidden to
__fcntl only.
* include/fcntl.h [IS_IN (rtld)]: Include <dl-fcntl.h> instead of
adding attribute_hidden to __open and __fcntl.
