there is chance that its "patch" version is empty. in that case, do not
include it in its version string. otherwise, we will have something
like:
Found gperftools:
GPERFTOOLS_TCMALLOC_LIBRARY;GPERFTOOLS_TCMALLOC_MINIMAL_LIBRARY;GPERFTOOLS_PROFILER_LIBRARY
(found version "2.4.#define TC_VERSION_PATCH """)
when running cmake
Signed-off-by: Kefu Chai <kchai@redhat.com>