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