Option to not include zstd and zlib

[gpalino]

I have an use case to compile an application, fetch the cpptrace and necessary libdwarf. But I don't need to produce compressed debug sections in DWARF format. So fetching and compiling zstd is a waste of time and space IMO. I added option CPPTRACE_ENABLE_DEBUG_DECOMPRESSION (which is default ON), to be able to disable fetching of zstd both in cpptrace and libdwarf.