[docs] Link to ORC APIs from JITLink

[cmcaine]

Summary

Literally adds one obvious link to the llvm sphinx docs.

This revision is really tiny because this is my first contribution and I am trying to learn the process.

[lhames]

LGTM. Thanks Colin!

What nam / email would you like me to use for the commit authorship?

[cmcaine]

Thanks!

"Colin Caine <[e-mail]>"

Would be fine.

[lhames]

Done. Thanks Colin!

llvm/docs/JITLink.rst

 
 This document aims to provide a high-level overview of the design and API
 of the JITLink library. It assumes some familiarity with linking and
 relocatable object files, but should not require deep expertise. If you know
 what a section, symbol, and relocation are you should find this document
 accessible. If it is not, please submit a patch (:doc:`Contributing`) or file a
 bug (:doc:`HowToSubmitABug`).
 
-JITLink is a library for :ref:`jit_linking`. It was built to support the ORC JIT
-APIs and is most commonly accessed via ORC's ObjectLinkingLayer API. JITLink was
+JITLink is a library for :ref:`jit_linking`. It was built to support the :doc:`ORC JIT
+APIs<ORCv2>` and is most commonly accessed via ORC's ObjectLinkingLayer API. JITLink was
 developed with the aim of supporting the full set of features provided by each
 object format; including static initializers, exception handling, thread local
 variables, and language runtime registration. Supporting these features enables
 ORC to execute code generated from source languages which rely on these features
 (e.g. C++ requires object format support for static initializers to support
 static constructors, eh-frame registration for exceptions, and TLV support for
 thread locals; Swift and Objective-C require language runtime registration for
 many features). For some object format features support is provided entirely