http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54124
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-07-30 11:37:18 UTC --- That section is formatted the same in HTML and the info pages. If you go to the options summary at http://gcc.gnu.org/onlinedocs/gcc-4.7.1/gcc/Option-Summary.html you can search for -dM (or "preprocessor") and find it in the relevant section, which takes you to http://gcc.gnu.org/onlinedocs/gcc-4.7.1/gcc/Preprocessor-Options.html
