Update kernel-features.h files for Linux 5.1.

Linux 5.1 adds missing syscalls to the syscall table for many Linux
kernel architectures.  This patch updates the kernel-features.h
headers accordingly.  __ASSUME_DIRECT_SYSVIPC_SYSCALLS is not updated
because of the differences between new and old syscalls described in
<https://sourceware.org/ml/libc-alpha/2019-05/msg00235.html>.  The
statfs64 structure used by alpha matches what the new kernel syscalls
use.

Tested with build-many-glibcs.py.

	* sysdeps/unix/sysv/linux/alpha/kernel-features.h
	(__ASSUME_STATFS64): Only undefine if [__LINUX_KERNEL_VERSION <
	0x050100].
	* sysdeps/unix/sysv/linux/ia64/kernel-features.h (__ASSUME_STATX):
	Likewise.
	* sysdeps/unix/sysv/linux/sh/kernel-features.h
	(__ASSUME_STATX): Likewise.