add_library(libxgboost SHARED ${SOURCES}) builds a library named
liblibxgboost.so; However, simply changing it to add_library(xgboost ...)
won't work, as add_executable(xgboost ...) and add_library(xgbboost ...)
will then have the same target name. This patch correctly handles the
same-name situation through SET_TARGET_PROPERTIES.
