Fix librt linking for wxWidgets

src/CMakeLists.txt

@@ -71,6 +71,12 @@ if (SLIC3R_GUI)
         list(APPEND wxWidgets_LIBRARIES ${EXPAT_LIBRARIES})
     endif ()
 
+    # This is an issue in the new wxWidgets cmake build, doesn't deal with librt
+    find_library(LIBRT rt)
+    if(LIBRT)
+        list(APPEND wxWidgets_LIBRARIES ${LIBRT})
+    endif()
+
 #    list(REMOVE_ITEM wxWidgets_LIBRARIES oleacc)
     message(STATUS "wx libs: ${wxWidgets_LIBRARIES}")