fix BUILD_VOICE_SUPPORT=OFF static build

[Syping]

Building DPP statically with BUILD_VOICE_SUPPORT=OFF fails with undefined targets (related to HAVE_VOICE), so i put these targets in a if condition.

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
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