CMP0025
-------

Compiler id for Apple Clang is now ``AppleClang``.

CMake 3.0 and above recognize that Apple Clang is a different compiler
than upstream Clang and that they have different version numbers.
CMake now prefers to present this to projects by setting the
:variable:`CMAKE_<LANG>_COMPILER_ID` variable to ``AppleClang`` instead
of ``Clang``.  However, existing projects may assume the compiler id for
Apple Clang is just ``Clang`` as it was in CMake versions prior to 3.0.
Therefore this policy determines for Apple Clang which compiler id to
report in the :variable:`CMAKE_<LANG>_COMPILER_ID` variable after
language ``<LANG>`` is enabled by the :command:`project` or
:command:`enable_language` command.  The policy must be set prior
to the invocation of either command.

The OLD behavior for this policy is to use compiler id ``Clang``.  The
NEW behavior for this policy is to use compiler id ``AppleClang``.

This policy was introduced in CMake version 3.0.  Use the
:command:`cmake_policy` command to set this policy to OLD or NEW explicitly.
Unlike most policies, CMake version |release| does *not* warn
by default when this policy is not set and simply uses OLD behavior.
See documentation of the
:variable:`CMAKE_POLICY_WARNING_CMP0025 <CMAKE_POLICY_WARNING_CMP<NNNN>>`
variable to control the warning.