texinfo: simplify reference emission.

The commit adds a new config value 'texinfo_emit_document_references'
that blocks the emission of inline references and make it better readable
with legacy stand-alone reader ``info``.

Before the change we emit:
Default option value for @ref{e,,-Wshift-overflow3}.

while with texinfo_emit_document_references == True:
Default option value for -Wshift-overflow3.

It addresses limitations mentioned in Sphinx' FAQ:
https://www.sphinx-doc.org/en/master/faq.html#texinfo-info

doc/_static/conf.py.txt

@@ -319,6 +319,10 @@ texinfo_documents = [
 #
 # texinfo_no_detailmenu = False
 
+# If false, do not generate in manual @ref nodes.
+#
+# texinfo_cross_references = False
+
 # -- A random example -----------------------------------------------------
 
 import sys, os