This is a dummy trivial example of how one could use conditional compilation flags in Makefiles.
The application is a simple Hello World that outputs "Release message" by default. But if compiled
with MY_DEBUG=1 environment variable, it outputs "Debug message" instead.
Caveat is that you need to manually track if there is an existing build in the source tree and
make clean it if you're changing the value of MY_DEBUG variable. The reason is that make
does not track flag values used during compilation and is not able to figure out that flags have
been changed by itself.
So the full flow is like this:
> make clean
> make
> ./src/example
Release message
> make clean
> MY_DEBUG=1 make
> ./src/example
Debug message