Fix __ASSUME_MLOCK2 for ARM, MicroBlaze (bug 23867).

The generic kernel-features.h defines __ASSUME_MLOCK2 for 4.4 and
later kernels.  However, for 32-bit ARM binaries running on 64-bit ARM
kernels, and for MicroBlaze, the syscall was only wired up in the 4.7
kernel.  (32-bit ARM kernels did have the syscall from 4.4 onwards.)
This patch duly arranges for the macro to be undefined for those
architectures for kernels before 4.7.

Tested with build-many-glibcs.py for its ARM and MicroBlaze
configurations.

	[BZ #23867]
	* sysdeps/unix/sysv/linux/arm/kernel-features.h
	[__LINUX_KERNEL_VERSION < 0x040700] (__ASSUME_MLOCK2): Undefine.
	* sysdeps/unix/sysv/linux/microblaze/kernel-features.h
	[__LINUX_KERNEL_VERSION < 0x040700] (__ASSUME_MLOCK2): Undefine.