set_target_properties used up until now in the SET_BIN_DIR macro sets
the INSTALL_RPATH property and discards whatever it contained before.
The INSTALL_RPATH target property is initialized with the cache variable
CMAKE_INSTALL_RPATH (possilbly given via the -D option of cmake). To
preserve this "default" value this commit replaced set_target_properties
with set_property(... APPEND ...).