As some of you might know, GCC 4.8 was released recently (http://gcc.gnu.org/gcc-4.8/changes.html). Therefore, the only logical thing to do was to compile WL with it and see what happened. This was done on a Debian Sid system (though gcc-4.8 is still in experimental so you need to add that repository).
The main change warning-wise seems to be that it warns about -Wunused-local-typedefs now. This seems to boil down to the macro in src/compile_assert.h which based on the comment in it is done that way to avoid shadow warnings. So I guess we should decide whether this code can be improved or whether we want to ignore the warning. (We have the macros to temporarily disable warnings, but I am not sure whether it would be sufficient to apply it in src/compile_assert.h or if we would need to sprinkle it across all places referring to it.)
I only skimmed the rest of the warnings, but they seem to mostly be the same as we get in older releases too.
PS. I filed this as a new bug since I consider bug 825957 as fixed when we became warning-free. After bug 1033615 we are no longer warning-free again, though I think it is better to split out the discussion for these warnings. Otherwise we will end up with a gigantic bug report covering everything which has been closed and reopened multiple times as warnings are removed and introduced.
PPS. See bug 1202101 for warnings generated in Visual Studio.
I vote for ignoring - c++11 comes with static_assert which replaces this compile time assert. Once we switch (which we will soonish - c++ 11 is adopted at a fast pace) this warning will go away as well.