doc: clean up PDF generation for ACRN docs

PRs #5945 and #5949 introduced fixes to the doc building process to
support PDF generation of the documentation set.  This PR refines the
doc build process, cleaning up the Makefile, adding display of tool
version information, and updates the doc building documentation to
include additional dependencies needed for building the PDF and
instructions for how to build the PDF.  The latexpdf make target is
provided to just run the latex and PDF producing process that depends on
the HTML artifacts from a make html run.  A new make pdf target is
provided that combines the two steps into one.

A new know-issues pattern file is added that verifies the expected
output from the latexpdf process is returned, as it can't be completely
eliminated without losing potential error messages that need to be
resolved.

Signed-off-by: David B. Kinder <david.b.kinder@intel.com>

doc/tutorials/docbuild.rst

@@ -139,10 +139,10 @@ different (newer) version of doxygen noted above that may also work.
 
 For Ubuntu use:
 
-  .. code-block:: bash
+.. code-block:: bash
 
-     sudo apt install doxygen python3-pip \
-       python3-wheel make graphviz xsltproc
+   sudo apt install doxygen python3-pip \
+     python3-wheel make graphviz xsltproc
 
 Then use ``pip3`` to install the remaining Python-based tools:
 
@@ -174,10 +174,24 @@ And with that you're ready to generate the documentation.
 
       doc/scripts/show-versions.py
 
+
+Extra Tools for Generating PDF
+==============================
+
+While the primary output for ACRN documentation is for an HTML website, you can
+also generate a PDF version of the documentation.  A few extra tools are needed
+only if you want to create PDF output.  For Ubuntu users add these additional
+packages:
+
+.. code-block:: bash
+
+   sudo apt install texlive-latex-recommended texlive-fonts-recommended \
+     texlive-latex-extra latexmk texlive-xetex xindy
+
 Documentation Presentation Theme
 ********************************
 
-Sphinx supports easy customization of the generated documentation
+Sphinx supports easy customization of the generated HTML documentation
 appearance through the use of themes.  Replace the theme files and do
 another ``make html`` and the output layout and style is changed. The
 sphinx build system creates document cache information that attempts to
@@ -196,11 +210,13 @@ Run the Documentation Processors
 
 The ``acrn-hypervisor/doc`` directory has all the ``.rst`` source files, extra
 tools, and ``Makefile`` for generating a local copy of the ACRN technical
-documentation.  For generating all the API documentation, there is a
+documentation. (Some additional ``.rst`` files and other material is extracted
+or generated from the ``/misc`` folder as part of the ``Makefile``.)
+For generating all the API documentation, there is a
 dependency on having the ``acrn-kernel`` repo's contents available too
 (as described previously).  You'll get a sphinx warning if that repo is
 not set up as described, but you can ignore that warning if you're
-not planning to publish.
+not planning to publish or show the API documentation.
 
 .. code-block:: bash
 
@@ -221,6 +237,36 @@ with the command:
 
 and use your web browser to open the URL:  ``http://localhost:8000``.
 
+Generate PDF Output
+===================
+
+After the HTML content is generated, it leaves artifacts behind that you can
+use to generate PDF output using the Sphinx ``latex`` builder.  This
+builder initially creates LaTeX output in the ``_build/latex`` folder and then
+uses the ``latexmk`` tool to create the final ``acrn.pdf`` file in the same
+folder.  This process automatically makes a few passes over the content to create the index
+and resolve intra-document hyperlinks, and produces plenty of progress messages along the
+way.  The Sphinx-generated output for tables and code blocks also yields many "underfill"
+and "overfill" messages from the ``latex`` builder that can't be easily
+suppressed or fixed.  Because of that, we recommend running this PDF generation
+with the ``-silent`` options, like this (after you've run ``make html``:
+
+.. code-block:: bash
+
+   make latexpdf LATEXMKOPTS="-silent"
+
+For convenience, we've also created a make target called ``pdf`` that will first
+generate the HTML content and then make the PDF file in one step:
+
+.. code-block:: bash
+
+   make pdf
+
+This make target runs quietly, and then verifies that no unexpected message from
+the build process are produced (using the :ref:`message filtering process
+<filter_expected>` explained below.  Either way, when the build completes, the
+generated PDF file is in ``_build/latex/acrn.pdf``.
+
 Publish Content
 ***************
 
@@ -299,6 +345,8 @@ of the repo, and add some extra flags to the ``make`` commands:
    make DOC_TAG=release RELEASE=2.3 html
    make DOC_TAG=release RELEASE=2.3 publish
 
+.. _filter_expected:
+
 Filter Expected Warnings
 ************************