[Flang][Docs] Fix warnings when building docs.

Following warning were seen with recommonmark(0.5.0) and sphinx(1.8.5).
`parser.py:75: UserWarning: Container node skipped: type=document warn("Container node skipped: type={0}".format(mdnode.t))`

The warnings are due to an issue in recommonmark's(a python package) older versions.
A better solution is to use the latest version of recommonmark(>=0.6.0) to avoid
these issue in the first place.
This patch fixes the warnings for older versions.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D91117

flang/docs/conf.py

@@ -11,6 +11,7 @@
 
 import sys, os
 from datetime import date
+from recommonmark.parser import CommonMarkParser
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -19,6 +20,13 @@ from datetime import date
 
 # -- General configuration -----------------------------------------------------
 
+# https://github.com/readthedocs/recommonmark/issues/177
+#Method used to remove the warning message.
+class CustomCommonMarkParser(CommonMarkParser):
+    def visit_document(self, node):
+        pass
+
+
 # If your documentation needs a minimal Sphinx version, state it here.
 #needs_sphinx = '1.0'
 # Add any Sphinx extension module names here, as strings. They can be extensions
@@ -44,7 +52,7 @@ else:
     # This requires 0.5 or later.
     extensions.append('recommonmark')
   else:
-    source_parsers = {'.md': 'recommonmark.parser.CommonMarkParser'}
+    source_parsers = {'.md': CustomCommonMarkParser}
   source_suffix['.md'] = 'markdown'
   extensions.append('sphinx_markdown_tables')
 

flang/docs/index.md

@@ -47,6 +47,7 @@ Flang is LLVM's Fortran frontend
    OptionComparison
    ParserCombinators
    RuntimeDescriptor
+   RuntimeTypeInfo
    Calls
    Character
    ArrayComposition