cmake: fix warning in FindLibUnwind.cmake

This patch fixes the following warning:

NO_WRAP
  CMake Warning (dev) at cmake-3.25/Modules/FindPackageHandleStandardArgs.cmake:438 (message):
    The package name passed to `find_package_handle_standard_args`
    (GetLIBUNWINDVersion.cmake) does not match the name of the calling package
    (LibUnwind).  This can lead to problems in calling code that expects
    `find_package` result variables (e.g., `_FOUND`) to follow a certain
    pattern.
  Call Stack (most recent call first):
    cmake/FindLibUnwind.cmake:82 (find_package_handle_standard_args)
    CMakeLists.txt:552 (find_package)
NO_WRAP

Closes #6998

NO_DOC=build
NO_TEST=build
NO_CHANGELOG=build