Update NEWS for MPX support in the dynamic linker

[Zamyatin, Igor]

> You need a blank line before the new item.  Two spaces between sentences.
> Don't mention dynamic linker internal function names, just the user-visible
> effects.  How about this?
> 
> * On x86, the dynamic linker's lazy-binding support is now compatible
>   with application code using Intel MPX instructions.  (With all
>   previous versions, the MPX register state could be clobbered when
>   making calls into or out of a shared library.)  Note that while the
>   new dynamic linker is compatible with all known x86 hardware whether
>   or not it supports Intel MPX, some x86 instruction-set emulators
>   might fail to handle the new instruction encodings.  This is known
>   to affect Valgrind versions prior to 3.9, and might affect other
>   tools that do instruction emulation.

Thought it should be less detailed :) But I like this, the only thing is that MPX is x86_64 oriented and as HJ already mentioned support in dynamic linker added for x86_64 so I suggest to change first mentioning of x86 on x86_64.

Thanks,
Igor