[XCore][docs] Fix XCore compiler writer documentation links.

[nigelp-xmos]

Summary

Fix links to XMOS website. Add link for XS2 architecture.

[nigelp-xmos]

Added reviewer suggestions from git history. If someone familiar with updating the documentation could commit for me, I would be grateful, as I do not have commit access.

[jryans]

Thanks for the update, this looks good to me. I'll work on committing the patch as well.

llvm/docs/CompilerWriterInfo.rst

 * `Intel 64 and IA-32 manuals <http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html>`_
 * `Intel Itanium documentation <http://www.intel.com/design/itanium/documentation.htm?iid=ipp_srvr_proc_itanium2+techdocs>`_
 * `X86 and X86-64 SysV psABI <https://github.com/hjl-tools/x86-psABI/wiki/X86-psABI>`_
 * `Calling conventions for different C++ compilers and operating systems  <http://www.agner.org/optimize/calling_conventions.pdf>`_
 
 XCore
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-* `The XMOS XS1 Architecture (ISA) <https://www.xmos.com/en/download/public/The-XMOS-XS1-Architecture%28X7879A%29.pdf>`_
-* `Tools Development Guide (includes ABI) <https://www.xmos.com/download/public/Tools-Development-Guide%28X9114A%29.pdf>`_
+* `The XMOS XS1 Architecture (ISA) <https://www.xmos.ai/download/The-XMOS-XS1-Architecture%281.0%29.pdf>`_
+* `The XMOS XS2 Architecture (ISA) <https://www.xmos.ai/download/xCORE-200:-The-XMOS-XS2-Architecture-%28ISA%29%281.1%29.pdf>`_
+* `Tools Development Guide (includes ABI) <https://www.xmos.ai/download/Tools-Development-Guide%282.1%29.pdf>`_
 
 Hexagon
 -------
 
 * `Hexagon Programmer's Reference Manuals and Hexagon ABI Specification (registration required, free sign-up) <https://developer.qualcomm.com/software/hexagon-dsp-sdk/tools>`_
 
 Other relevant lists
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