AODNative: link Threads::Threads publicly

Decoder.cxx and test_ReadPlan.cxx use std::thread, but neither the
library nor its test executable linked the threads library. With
glibc < 2.34 (e.g. EL8/slc8) pthread_* live in libpthread, so linking
fails with -Wl,--no-undefined:

  libO2AODNative.so: undefined reference to `pthread_create'
  o2-test-framework-aod-native: undefined reference to symbol
    'pthread_join@@GLIBC_2.2.5' / DSO missing from command line

Newer glibc merges libpthread into libc, which hides the problem there.
Make Threads::Threads a public dependency so all consumers get it.

Author: mhemmer-cern

Framework/AODNative/CMakeLists.txt

@@ -22,7 +22,7 @@ o2_add_library(AODNative
                        src/ReadPlan.cxx
                TARGETVARNAME targetName
                PRIVATE_INCLUDE_DIRECTORIES ${CMAKE_CURRENT_LIST_DIR}/src
-               PUBLIC_LINK_LIBRARIES Arrow::arrow_shared
+               PUBLIC_LINK_LIBRARIES Arrow::arrow_shared Threads::Threads
                PRIVATE_LINK_LIBRARIES PkgConfig::zstd PkgConfig::lz4 PkgConfig::lzma ZLIB::ZLIB)
 
 # Reading over root:// needs the XRootD client, which does not depend on ROOT.