Correct SH kernel-features.h undefines (bug 23862).

Correct SH kernel-features.h undefines (bug 23862).

The SH kernel-features.h undefines __ASSUME_RENAMEAT2 for kernel
versions before 4.8, but fails to undefine __ASSUME_EXECVEAT,
__ASSUME_MLOCK2 and __ASSUME_COPY_FILE_RANGE, although all those
syscalls (and several others) were added for SH in the same Linux
kernel commit (first released in 4.8).  This patch adds the proper
undefines of those macros.

Tested with build-many-glibcs.py for its SH configurations.

	[BZ #23862]
	* sysdeps/unix/sysv/linux/sh/kernel-features.h
	[__LINUX_KERNEL_VERSION < 0x040800] (__ASSUME_EXECVEAT): Undefine.
	[__LINUX_KERNEL_VERSION < 0x040800] (__ASSUME_MLOCK2): Likewise.
	[__LINUX_KERNEL_VERSION < 0x040800] (__ASSUME_COPY_FILE_RANGE):
	Likewise.