LIBXML2_LIBRARIES set using generator expressions for 21.2.9 and above

Starting in 21.2.9, the CMake variable LIBXML2_LIBRARIES gets set using generator expressions (e.g. $<BUILD_INTERFACE:/usr/lib64/libxml2.so>;$<INSTALL_INTERFACE:/usr/lib64/libxml2.so>) instead of the bare path that it gets set to in 21.2.8 or prior (e.g. /usr/lib64/libxml2.so).

Due to this fact, the generation of definitions.h in QFramework during configuration time fails. This is the only (known) issue preventing us from building CAFCore with the latest AnalysisBase release (currently already 21.2.23), so we should try and get this sorted out soon!