Restore support for TARGET_OBJECTS in link interfaces with unity builds

This was broken by commit df08c37a42 (cmGlobalGenerator: Add unity/pch
sources after computing compile features, 2024-02-02, v3.28.3~1^2~1^2),
and 3.28.2's commit 76b5383123 (cmGlobalGenerator: add unity sources
after computing target compile features, 2024-01-01, v3.28.2~17^2~1).

The problem is very similar to that fixed by commit 4e8f24e977 (PCH:
Clear link interface cache when adding PCH object to it, 2022-01-24,
v3.23.0-rc1~44^2~9).  Generalize that fix.

Fixes: #25696

Source/cmGeneratorTarget.h

@@ -721,7 +721,10 @@ public:
    */
   void ClearSourcesCache();
 
-  // Do not use.  This is only for a specific call site with a FIXME comment.
+  /**
+   * Clears cached evaluations of INTERFACE_LINK_LIBRARIES.
+   * They will be recomputed on demand.
+   */
   void ClearLinkInterfaceCache();
 
   void AddSource(const std::string& src, bool before = false);