[lldb] Fix the man page build

[teemperor]

Summary

In D94489 we changed the way we build the docs and now have some additional dependencies
to generate the Python API docs. As the same sphinx project is generating the man pages for
LLDB it should have in theory the same setup code that sets up the mocked LLDB module.

However, as we don't have that setup code the man page generation just fails as there
is no mocked LLDB module and the Python API generation errors out.

The man page anyway doesn't cover the Python API so I don't think there is any point
of going through the whole process (and requiring the sphinx plugins) just to generate
the (eventually unused) Python docs.

This patch just skips the relevant Python API generation when we are building the
man page.

[JDevlieghere]

LGTM

lldb/docs/conf.py

 #
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 from __future__ import print_function
 
 import sys, os, re
 from datetime import date
 
+building_man_page = tags.has('builder-man')
+
+# For the website we need to setup the path to the generated LLDB module that
+# we can generate documentation for its API.
+if not building_man_page:
     # 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
     # documentation root, use os.path.abspath to make it absolute, like shown here.
 
     # Add the current directory that contains the mock _lldb native module which
     # is imported by the `lldb` module.
     sys.path.insert(0, os.path.abspath("."))
     # Add the build directory that contains the `lldb` module. LLDB_SWIG_MODULE is
     # set by CMake.
     sys.path.insert(0, os.getenv("LLDB_SWIG_MODULE"))
 
 # Put the generated Python API documentation in the 'python_api' folder. This
 # also defines the URL these files will have in the generated website.
 automodapi_toctreedirnm = 'python_api'
 
 # -- General configuration -----------------------------------------------------
 
 # 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
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
-extensions = ['sphinx.ext.todo', 'sphinx.ext.mathjax', 'sphinx.ext.intersphinx',
-              'sphinx_automodapi.automodapi']
+extensions = ['sphinx.ext.todo', 'sphinx.ext.mathjax', 'sphinx.ext.intersphinx']
+
+# Unless we only generate the basic manpage we need the plugin for generating
+# the Python API documentation.
+if not building_man_page:
+    extensions.append('sphinx_automodapi.automodapi')
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
 
 # The suffix of source filenames.
 source_suffix = {
     '.rst': 'restructuredtext',
 }
 
 try:
   import recommonmark
 except ImportError:
   # manpages do not use any .md sources
-  if not tags.has('builder-man'):
+  if not building_man_page:
     raise
 else:
   import sphinx
   if sphinx.version_info >= (3, 0):
     # This requires 0.5 or later.
     extensions.append('recommonmark')
   else:
     source_parsers = {'.md': 'recommonmark.parser.CommonMarkParser'}

 # non-false value, then it is used:
 #today = ''
 # Else, today_fmt is used as the format for a strftime call.
 #today_fmt = '%B %d, %Y'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 exclude_patterns = ['_build', 'analyzer']
-
+# Ignore the generated Python documentation that is only used on the website.
+# Without this we will get a lot of warnings about doc pages that aren't
+# included by any doctree (as the manpage ignores those pages but they are
+# potentially still around from a previous website generation).
+if building_man_page:
+    exclude_patterns.append(automodapi_toctreedirnm)
 # Use the recommended 'any' rule so that referencing SB API classes is possible
 # by just writing `SBData`.
 default_role = 'any'
 
 # If true, '()' will be appended to :func: etc. cross-reference text.
 #add_function_parentheses = True
 
 # If true, the current module name will be prepended to all description