It started out as busywork, but it does many separate things. If I could
start over, I'd take them apart into multiple commits:
1. Remove G_ENABLE_DEBUG around GDK_DEBUG_*() calls
This is not needed at all, the calls themselves take care of it.
2. Remove G_ENABLE_DEBUG around profiling code
This now enables profiling support in release builds.
3. Stop poking _gdk_debug_flags and use GDK_DEBUG_CHECK()
This was old code that was never updated.
4. Make !G_ENABLE_DEBUG turn off GDK_DEBUG_CHECK()
The code used to
#define GDK_DEBUG_CHECK(...) false
#define GDK_DEBUG(...)
which would compile away all the code inside those macros. This
means a lot of variable definitions and debug utility functions
would suddenly no longer be used and cause compiler errors.
