Add missing CPP files to Make file, fixes #8731

[lumbric]

Fixes build errors occurring when AUTO_BED_LEVELING_UBL is enabled.

[thinkyhead]

What happens if MESH_BED_LEVELING is enabled when building with the Makefile? How about if we enable MAX7219_DEBUG, PCA9632, and I2C_POSITION_ENCODERS?

Do we basically need to include every .cpp file in Marlin in CXXSRC?

[lumbric]

Uh yes, you are right, the commit fixes the build only for my specific situation. I stopped adding cpp files, when I my configuration was building, but probably a generic solution would be better.
I don't think there is an easy way to determine which .cpp files are going to be needed without compiling them? Always compiling all .cpp files feels a bit of a wasted build time. But I guess it should be possible to make the .cpp files almost empty by using macros (if the feature is disabled which is implemented in this .cpp file).

What do you think? Any better suggestions or objections?

[thinkyhead]

Arduino IDE and PlatformIO compile all .cpp files in the project folder, so the Makefile should too. Here's how to do it without needing to list every file:

https://stackoverflow.com/questions/2908057/can-i-compile-all-cpp-files-in-src-to-os-in-obj-then-link-to-binary-in

[lumbric]

I have updated the fix. Now all *.cpp files are compiled.

[thinkyhead]

Magic!