[tiff] unused CMake variable CMAKE_DEBUG_POSTFIX

[Be-ing]

Host Environment

• OS: x64-linux (Fedora 34)
• Compiler: GCC 11.2.1

To Reproduce
Steps to reproduce the behavior:
./vcpkg install tiff

Failure logs

Building package tiff[core,jpeg,lzma,zip]:x64-linux...
-- Downloading https://download.osgeo.org/libtiff/tiff-4.3.0.tar.gz -> tiff-4.3.0.tar.gz...
-- Extracting source /home/be/sw/vcpkg/downloads/tiff-4.3.0.tar.gz
-- Applying patch cmakelists.patch
-- Applying patch fix-pkgconfig.patch
-- Applying patch FindCMath.patch
-- Using source at /home/be/sw/vcpkg/buildtrees/tiff/src/4.3.0-84bf77f2fa.clean
-- Found external ninja('1.10.2').
-- Configuring x64-linux-dbg
-- Configuring x64-linux-rel
CMake Warning at /home/be/sw/tenacity/build/vcpkg_installed/x64-linux/share/vcpkg-cmake/vcpkg_cmake_configure.cmake:472 (message):
  The following variables are not used in CMakeLists.txt:

      CMAKE_DEBUG_POSTFIX

  Please recheck them and remove the unnecessary options from the
  `vcpkg_cmake_configure` call.

  If these options should still be passed for whatever reason, please use the
  `MAYBE_UNUSED_VARIABLES` argument.
Call Stack (most recent call first):
  ports/tiff/portfile.cmake:42 (vcpkg_cmake_configure)
  scripts/ports.cmake:141 (include)

[dg0yt]

Please stop opening issues for "unused variables". It is not a failure. It is a new check to support maintainers, to be handled when making changes to a port.
And last not least, CMAKE_DEBUG_POSTFIX is a false positive.

[JackBoosY]

All the variables have prefix CMAKE_ should be ignored.

[JonLiu1993]

Fixed by PR #23864.