docs/conf.py: Suppress sphinx highlighting failure warnings

[MatzeB]

Summary

I cannot build the llvm documentation on my machine because the pygments syntax highlighting package used by sphinx fails to parse newer LLVM constructs or valid (looks valid to me) gas constructs like .secrel32 _function_name + 0. Disable this particular warning so the build doesn't abort.

I assume the llvm-sphinx-docs buildbot is still using sphinx-1.4 which didn't have this warning yet.

[hans]

lgtm

llvm/trunk/docs/conf.py

with open(os.path.join(command_guide_path, name)) as f:
         man_pages.append((file_subpath.replace('.rst',''), name,
                           description, man_page_authors, 1))
 
 # If true, show URL addresses after external links.
 #man_show_urls = False
 
 # FIXME: Define intersphinx configuration.
 intersphinx_mapping = {}
+
+# Pygment lexer are sometimes out of date (when parsing LLVM for example) or
+# wrong. Suppress the warning so the build doesn't abort.
+suppress_warnings = [ 'misc.highlighting_failure' ]