Revert [clang-shlib] Fix clang-shlib for PRIVATE dependencies

This reverts r365825 (git commit 3173c60f96c3ccfc17d403a192ae58e720153c23)

This is breaking BUILD_SHARED_LIBS=ON builds. Reverting while I rethink it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@365922 91177308-0d34-0410-b5e6-96231b3b80d8

tools/clang-shlib/CMakeLists.txt

@@ -7,35 +7,8 @@ get_property(clang_libs GLOBAL PROPERTY CLANG_STATIC_LIBS)
 
 foreach (lib ${clang_libs})
   list(APPEND _OBJECTS $<TARGET_OBJECTS:obj.${lib}>)
-  # Use the static library for its dependencies. The objects that constitute the
-  # static library will appear on the link line before the library, so it'll
-  # just be ignored, but the dependencies of the library will still be linked
-  # correctly.
-  #
-  # We could propagate the dependencies manually using the library's
-  # INTERFACE_LINK_LIBRARIES property, but that will contain $<LINK_ONLY:...>
-  # generator expressions if a static library has a private dependency, so we
-  # can't use a $<TARGET_PROPERTY:...> generator expression to get the property
-  # (since it wouldn't evaluate any generator expressions inside the property).
-  # We could use get_property and do string manipulation to manually evaluate
-  # the $<LINK_ONLY:...>, but that would miss any dependencies added after we
-  # evaluate the get_property. We could also use the LINK_LIBRARIES property
-  # instead, which should be free of any generator expressions, but that's
-  # technically incorrect (it'd most likely work fine in practice, but still).
-  #
-  # Another alternative would be to use --whole-archive or equivalent instead of
-  # using the object library at all. However, CMake reorders static libraries on
-  # the link line so that a library appears after all its dependents, which can
-  # reorder static libraries out of their --whole-archive --no-whole-archive
-  # sandwich. It's really hard to avoid that reordering while still propagating
-  # dependencies, which defeats the whole point.
-  #
-  # The ideal solution here is to bump our minimum CMake requirement to 3.12,
-  # which adds support for dependencies on object libraries. Until then, linking
-  # both the object and the static libraries seems like the least bad solution.
-  #
-  # TODO: Rework this when we bump our minimum CMake version to 3.12 or newer.
-  list(APPEND _DEPS ${lib})
+  list(APPEND _DEPS $<TARGET_PROPERTY:${lib},INTERFACE_LINK_LIBRARIES>)
+  list(APPEND _DEPS $<TARGET_PROPERTY:${lib},LINK_LIBRARIES>)
 endforeach ()
 
 if (CLANG_LINK_CLANG_DYLIB)