cmComputeLinkInformation: Track targets named by TARGET_OBJECTS sources

Since commit b6a5382217 (Ninja: depend on language module information
files directly, 2023-02-10, v3.27.0-rc1~502^2), the return value of
`cmCommonTargetGenerator::GetLinkedTargetDirectories` must account for
linked object libraries because they may provide modules (#25112).
These were added by commit b665966933 (cmComputeLinkInformation: track
OBJECT library dependencies, 2023-07-22, v3.27.1~5^2).  However, targets
named by `$<TARGET_OBJECTS:...>` sources are also needed (#25365).

The latter were added by commit 22da18b995 (Fortran: Restore support for
TARGET_OBJECTS providing modules, 2023-10-27, v3.28.0-rc4~9^2) and
commit 035302b7e3 (cmComputeLinkDepends: also copy the target from
object link items, 2023-10-27, v3.28.0-rc4~9^2~2).  However, their
approach added link entries not actually specified by projects.  It also
incorrectly re-used `cmComputeLinkDepends::AddLinkObject` for object
library targets when it is meant for their individual object files.
These problems caused additional regressions (#25417).  Revert the
implementation parts of those commits and leave behind an assertion and
comment to help avoid the mistake in the future.  Instead, track targets
named by `$<TARGET_OBJECTS:...>` sources with a dedicated member.

Issue: #25112
Issue: #25365
Fixes: #25417
Co-authored-by: Ben Boeckel <ben.boeckel@kitware.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/Source/cmCommonTargetGenerator.cxx b/Source/cmCommonTargetGenerator.cxx
index e9233b6..a5536d0 100644
--- a/Source/cmCommonTargetGenerator.cxx
+++ b/Source/cmCommonTargetGenerator.cxx
@@ -200,6 +200,9 @@ std::vector<std::string> cmCommonTargetGenerator::GetLinkedTargetDirectories(
     for (cmGeneratorTarget const* target : cli->GetObjectLibrariesLinked()) {
       addLinkedTarget(target);
     }
+    for (cmGeneratorTarget const* target : cli->GetExternalObjectTargets()) {
+      addLinkedTarget(target);
+    }
   }
   return dirs;
 }