Documentation: convert WritingAnLLVMPass.html to reST.

Patch by Anthony Mykhailenko with small fixes by me.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169992 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/WritingAnLLVMBackend.rst b/docs/WritingAnLLVMBackend.rst
index 7803163..7e243fa 100644
--- a/docs/WritingAnLLVMBackend.rst
+++ b/docs/WritingAnLLVMBackend.rst
@@ -54,8 +54,8 @@
   file (``.td`` suffix) and generates C++ code that can be used for code
   generation.
 
-* `Writing an LLVM Pass <WritingAnLLVMPass.html>`_ --- The assembly printer is
-  a ``FunctionPass``, as are several SelectionDAG processing steps.
+* :doc:`WritingAnLLVMPass` --- The assembly printer is a ``FunctionPass``, as
+  are several ``SelectionDAG`` processing steps.
 
 To follow the SPARC examples in this document, have a copy of `The SPARC
 Architecture Manual, Version 8 <http://www.sparc.org/standards/V8.pdf>`_ for