Just a short one.
Reference: http://stackoverflow.com/questions/4548702/whats-the-equivalent-of-cpp-dd-for-clang
Gives you list of all symbols defined by compilers. It’s interesting, that you have to feed it something (anything blank) to get this output though. /dev/null, or pipe in a blank echo (echo "” | gcc -dM -E -), etc.
Works with NaCl (pnacl-clang), Emscripten (emcc), and pretty much every GCC toolchain known to man.