build/cmake: add private dependencies back

Change-Id: Id95f38453043a2b8daa75918998800bf16eb41c9

CMakeLists.txt

@@ -125,6 +125,7 @@ if (DHTNET_PUPNP AND NOT MSVC)
         set(DHTNET_PUPNP Off)
     else()
         set(upnp_LIBRARIES PkgConfig::upnp)
+        set (requiresprivate "${requiresprivate} libupnp")
     endif()
 endif()
 if (DHTNET_NATPMP AND NOT MSVC)
@@ -136,6 +137,7 @@ if (DHTNET_NATPMP AND NOT MSVC)
             set(DHTNET_NATPMP Off)
         else()
             message("NAT-PMP found: ${natpmp_LIBRARIES}")
+            set (libsprivate "${libsprivate} -lnatpmp")
         endif()
     endif()
 endif()