use vt compilation flags for bundled libraries as well

[cz4rs]

Describe the bug
icpx build is showing following warnings:

/vt/lib/EngFormat-Cpp/src/eng_format.cpp:144:15: warning: comparison with NaN always evaluates to false in fast floating point modes [-Wtautological-constant-compare]
    if      ( std::isnan( value ) ) return "NaN";
              ^~~~~~~~~~~~~~~~~~~
/vt/lib/EngFormat-Cpp/src/eng_format.cpp:145:15: warning: comparison with infinity always evaluates to false in fast floating point modes [-Wtautological-constant-compare]
    else if ( std::isinf( value ) ) return "INFINITE";
              ^~~~~~~~~~~~~~~~~~~
2 warnings generated.

This is because we only set the project's common compiler flags to vt target:

$ git grep set_darma_compiler_flags
cmake-modules/SetCXXCompilerFlags.cmake:3:macro(set_darma_compiler_flags vt_target)
src/CMakeLists.txt:243:set_darma_compiler_flags(${VIRTUAL_TRANSPORT_LIBRARY})

Expected behavior
Use the same (or as similar as possible) set of flags for bundled libraries as for vt.