use lib install dir defined by GNUInstallDirs

this should fix library search problems on Tumbleweed

CMakeLists.txt

@@ -77,10 +77,11 @@ include(cmake/enable_doxygen_documentation.cmake)
 include(cmake/enable_code_style_check.cmake)
 
 # Install the library and the executables
+# this defines architecture-dependent ${CMAKE_INSTALL_LIBDIR}
+include(GNUInstallDirs)
 install( TARGETS ${PROJECT_NAME} 
     EXPORT ${PROJECT_NAME}Targets
-    RUNTIME DESTINATION bin 
-    LIBRARY DESTINATION lib )
+    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR} )
 
 # all include files go into include/PROJECT_NAME
 # The exclusion of ${PROJECT_NAME} prevents the recursive installation of the files just being installed.