Just a short one.

Reference: http://stackoverflow.com/questions/4548702/whats-the-equivalent-of-cpp-dd-for-clang

clang -dM -E - < /dev/null
clang++ -dM -E - < /dev/null
gcc -dM -E - < /dev/null
g++ -dM -E - < /dev/null
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.