Compiler warnings needs tuned from defaults

[nkolban]

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When we compile Sketches for the Pi using the current build system, we end up with failures when importing some libraries and sketches. It appears that the compiler warning levels need tuned for compatibility with what is the "norm" in a real Arduino environment. This issue will capture, log, discuss and address these considerations.

[nkolban]

-Wstrict-aliasing When compiling the Adafruit GFX library we ran foul of this entry. A quick check shows that this is related to the optimization level. We are currently using -O3. I suggest we switch off optimization.

[nkolban]

-Wint-to-pointer-cast It appears that we can disable this warning with -Wno-int-to-pointer-cast.

[nkolban]

-Wunused-variable This may be only a warning and can be left in.

[me-no-dev]

-Wint-to-pointer-cast << what did you compile to get this?