Linking: Optionally reorder direct dependencies from LINK_LIBRARIES

Traditionally CMake generates link lines by starting with the direct
link dependencies specified by `LINK_LIBRARIES` in their original order
and then appending indirect dependencies that the direct dependencies
do not express.  This gives projects control over ordering among
independent entries, which can be important when intermixing flags
and libraries, or when multiple libraries provide the same symbol.
However, it may also result in inefficient link lines.

Add support for an alternative strategy that can reorder direct link
dependencies to produce more efficient link lines.  This is useful
for projects that cannot easily specify their targets' direct
dependencies in an order that satisfies indirect dependencies.

Add a `CMAKE_LINK_LIBRARIES_STRATEGY` variable and corresponding
`LINK_LIBRARIES_STRATEGY` target property to select a strategy.

Fixes: #26271

Help/variable/CMAKE_LINK_LIBRARIES_STRATEGY.rst

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+CMAKE_LINK_LIBRARIES_STRATEGY
+-----------------------------
+
+.. versionadded:: 3.31
+
+Specify a strategy for ordering targets' direct link dependencies
+on linker command lines.
+
+The value of this variable initializes the :prop_tgt:`LINK_LIBRARIES_STRATEGY`
+target property of targets as they are created.  Set that property directly
+to specify a strategy for a single target.
+
+CMake generates a target's link line using its :ref:`Target Link Properties`.
+In particular, the :prop_tgt:`LINK_LIBRARIES` target property records the
+target's direct link dependencies, typically populated by calls to
+:command:`target_link_libraries`.  Indirect link dependencies are
+propagated from those entries of :prop_tgt:`LINK_LIBRARIES` that name
+library targets by following the transitive closure of their
+:prop_tgt:`INTERFACE_LINK_LIBRARIES` properties.  CMake supports multiple
+strategies for passing direct and indirect link dependencies to the linker.
+
+Consider this example for the strategies below:
+
+.. code-block:: cmake
+
+  add_library(A STATIC ...)
+  add_library(B STATIC ...)
+  add_library(C STATIC ...)
+  add_executable(main ...)
+  target_link_libraries(B PRIVATE A)
+  target_link_libraries(C PRIVATE A)
+  target_link_libraries(main PRIVATE A B C)
+
+The supported strategies are:
+
+``PRESERVE_ORDER``
+  Entries of :prop_tgt:`LINK_LIBRARIES` always appear first and in their
+  original order.  Indirect link dependencies not satisfied by the
+  original entries may be reordered and de-duplicated with respect to
+  one another, but are always appended after the original entries.
+  This may result in less efficient link lines, but gives projects
+  control of ordering among independent entries.  Such control may be
+  important when intermixing link flags with libraries, or when multiple
+  libraries provide a given symbol.
+
+  This is the default.
+
+  In the above example, this strategy computes a link line for ``main``
+  by starting with its original entries ``A B C``, and then appends
+  another ``A`` to satisfy the dependencies of ``B`` and ``C`` on ``A``.
+  The final order is ``A B C A``.
+
+``REORDER``
+  Entries of :prop_tgt:`LINK_LIBRARIES` may be reordered, de-duplicated,
+  and intermixed with indirect link dependencies.  This may result in
+  more efficient link lines, but does not give projects any control of
+  ordering among independent entries.
+
+  In the above example, this strategy computes a link line for ``main``
+  by re-ordering its original entries ``A B C`` to satisfy the
+  dependencies of ``B`` and ``C`` on ``A``.
+  The final order is ``B C A``.
+
+.. note::
+
+  Regardless of the strategy used, the actual linker invocation for
+  some platforms may de-duplicate entries based on linker capabilities.
+  See policy :policy:`CMP0156`.