Rather than inspecting CMAKE_BUILD_TYPE manually and setting
DEBUG_OPTIONS based off the results, set CMAKE_{C/CXX}_FLAGS_DEBUG,
and allow that to be picked up by CMake #565. Remove repeated -W
flags that were all over the place, making them global compiler
flags. Remove repeated FORTIFY=2 definition that was all over the
place, making it a global compiler definition. Remove all uses of
${DEBUG_FLAGS}. Also, since CMake doesn't define a CMAKE_BUILD_TYPE
by default, instead just setting neither debugging nor optimization
flags, in what seems a pretty fucking boneheaded move, set it by
default to RelWithDebInfo. ugh. Explicitly disuse unused PoC variables.
