Retire HAVE_IOCTL_* configure checks

The HAVE_IOCTL_* configure checks were originally added for
compatibility with an ancient version of glibc.  This support
and additional complexity is no longer needed and is therefore
being removed.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Closes openzfs#585

config/user.m4

@@ -7,7 +7,6 @@ AC_DEFUN([ZFS_AC_CONFIG_USER], [
 	ZFS_AC_CONFIG_USER_SYSVINIT
 	ZFS_AC_CONFIG_USER_DRACUT
 	ZFS_AC_CONFIG_USER_ARCH
-	ZFS_AC_CONFIG_USER_IOCTL
 	ZFS_AC_CONFIG_USER_ZLIB
 	ZFS_AC_CONFIG_USER_LIBUUID
 	ZFS_AC_CONFIG_USER_LIBBLKID

lib/libspl/include/unistd.h

@@ -29,15 +29,7 @@
 #ifndef _LIBSPL_UNISTD_H
 #define	_LIBSPL_UNISTD_H
 
-#if !defined(HAVE_IOCTL_IN_UNISTD_H)
-#if defined(HAVE_IOCTL_IN_SYS_IOCTL_H)
 #include <sys/ioctl.h>
-#elif defined(HAVE_IOCTL_IN_STROPTS_H)
-#include <stropts.h>
-#else /* HAVE_IOCTL_IN_STROPTS_H */
-#error "System call ioctl() unavailable"
-#endif /* HAVE_IOCTL_IN_SYS_IOCTL_H */
-#endif /* !HAVE_IOCTL_IN_UNISTD_H */
 
 #if !defined(HAVE_ISSETUGID)
 #include <sys/types.h>