This PR adds a new set of debug macros that allow a certain code to be
only executed when certain debug conditions are met. This is useful to
guard things that are not strictly messages but compute and store things
that are related to those messages.
Strictly speaking the existing ODBG_OS could be used as well but that
requires a stream object to be created which is unnecessary in some
cases.
Example of how it works:
```cpp
ODBG_IF("Counters", [&](uint32_t Level) {
someCounter++;
if (Level == 2) moreDetailedCounter += f();
});
ODBG("Counters") << "Counter" = someCounter
<< ODBG_IF(2) << "DetailedCounter" << moreDetailedCounter;
```
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