Fix CMake compile definition leakage

[Alloyed]

My CI build was failing, and near as I can tell it's because I declare my targets, then import libdaisy. so the add_compile_definitions doesn't end up applying to my targets. marking it as public like this makes it transitive, so anybody that links to libdaisy also has this compile definition.

from my CI:

[ 92%] Building CXX object calibrate/CMakeFiles/Calibrate.dir/calibrate.cpp.obj
In file included from /home/runner/work/KitsBlips/KitsBlips/sdk/libDaisy/src/daisy.h:78,
                 from /home/runner/work/KitsBlips/KitsBlips/sdk/libDaisy/src/daisy_patch_sm.h:3,
                 from /home/runner/work/KitsBlips/KitsBlips/daisy/calibrate/calibrate.cpp:1:
/home/runner/work/KitsBlips/KitsBlips/sdk/libDaisy/src/util/WavPlayer.h: In member function 'daisy::WavPlayer<workspace_bytes>::Result daisy::WavPlayer<workspace_bytes>::Open(const char*)':
/home/runner/work/KitsBlips/KitsBlips/sdk/libDaisy/src/util/WavPlayer.h:95:16: error: 'FileReader' is not a member of 'daisy'; did you mean 'IReader'?
   95 |         daisy::FileReader reader(&file_);
      |                ^~~~~~~~~~
      |                IReader
/home/runner/work/KitsBlips/KitsBlips/sdk/libDaisy/src/util/WavPlayer.h:97:26: error: 'reader' was not declared in this scope; did you mean 'IReader'?
   97 |         if(!parser.parse(reader))
      |                          ^~~~~~
      |                          IReader
gmake[2]: *** [calibrate/CMakeFiles/Calibrate.dir/build.make:79: calibrate/CMakeFiles/Calibrate.dir/calibrate.cpp.obj] Error 1

[stephenhensley]

Confirmed that I could recreate your issue, and that your fix gets things compiling.

Not directly related, but I did notice that when building the WavParser example (both inside the libDaisy repo, and as a new project outside of the repo) w/ CMAKE_BUILD_TYPE=Release that things didn't work as expected. Building w/ Debug instead worked fine.

Not sure if you ran into anything similar, but something that I'll keep an eye out for (I'm trying to use the CMake build more on newer projects).

Thanks for the contribution!