Fix sh4 build with __ASSUME_ST_INO_64_BIT redefinition

Fix sh4 build with __ASSUME_ST_INO_64_BIT redefinition

Since 327792c sh4 builds fails with:

../sysdeps/unix/sysv/linux/kernel-features.h:49:0: error: "__ASSUME_ST_INO_64_BIT" redefined [-Werror]
 #define __ASSUME_ST_INO_64_BIT  1
 ^
In file included from ../sysdeps/unix/sysv/linux/sysdep.h:19:0,
                 from ../sysdeps/unix/sysv/linux/sh/sysdep.h:24,
                 from ../sysdeps/unix/sysv/linux/sh/sh4/sysdep.h:4,
                 from <stdin>:1:
../sysdeps/unix/sysv/linux/sh/kernel-features.h:47:0: note: this is the location of the previous definition
 #define __ASSUME_ST_INO_64_BIT 0

It is because sh4 kernel-features.sh is included multiple times
without guards and this patch fixes by adding them.

Tested on a sh4-linux-gnu build.

	* sysdeps/unix/sysv/linux/sh/kernel-features.h: Add include
	guards.