Introduce debug/debug-only
opt
can let the user choose what kind of debug output they want, this commits introduce a similar option interacting with LLVM's debug system.
This lets us do things like this:
#define DEBUG_TYPE "mydebug"
LLVM_DEBUG(dbgs() << "some debug string\n");
and later call parcoach -debug
to have all debug outputs, or parcoach -debug-only "mydebug,someotherdebug"
to have only debug output related to a specific module from parcoach.
And obviously all this is a no-op when compiling in release mode!