Unity Build: Add option for generating per-file unique id

Help/manual/cmake-properties.7.rst

Help/manual/cmake-variables.7.rst

Help/prop_tgt/UNITY_BUILD.rst

Help/prop_tgt/UNITY_BUILD_UNIQUE_ID.rst

Help/release/dev/unity-build-anonymous-macros.rst

Help/variable/CMAKE_UNITY_BUILD_UNIQUE_ID.rst

Source/cmLocalGenerator.cxx

Source/cmTarget.cxx

Tests/RunCMake/UnityBuild/RunCMakeTest.cmake

Tests/RunCMake/UnityBuild/unitybuild_anon_ns.cmake

...s/RunCMake/UnityBuild/unitybuild_anon_ns_group_mode.cmake

...nCMake/UnityBuild/unitybuild_anon_ns_no_unity_build.cmake

...s/RunCMake/UnityBuild/unitybuild_anon_ns_test_files.cmake