build: Do not expose dependency to dpdk in installed cmake files

seastar currently includes the objects of the dpdk library to within its
static library. As a result, dpdk library may as well not exist to
outside users - it is effectively an implementation detail.

Unfortunately it is exposed in the INTERFACE_LINK_LIBRARIES list of the
installed Seastar::seastar target.

This is a known problem in CMake
https://gitlab.kitware.com/cmake/cmake/-/issues/15415 and the solution
is to use BUILD_INTERFACE generator expression.

Co-authored-by: Kefu Chai <[email protected]>

Author: p12tic

Diff for: CMakeLists.txt

@@ -875,9 +875,16 @@ else ()
 endif ()
 
 if (Seastar_DPDK)
+  # Although Seastar uses DPDK internally, DPDK symbols should not be exposed to
+  # Seastar users. However, DPDK's dependencies (like numa, pthread) must still
+  # be included in Seastar's INTERFACE_LINK_LIBRARIES to ensure proper linking
+  # of applications using Seastar.
   target_link_libraries (seastar
     PRIVATE
-      DPDK::dpdk)
+      "$<BUILD_INTERFACE:DPDK::dpdk>")
+  get_target_property(DPDK_INTERFACE_LINK_LIBRARIES DPDK::dpdk INTERFACE_LINK_LIBRARIES)
+  target_link_libraries (seastar
+    PRIVATE "${DPDK_INTERFACE_LINK_LIBRARIES}")
 endif ()
 
 include (TriStateOption)