FindLibArchive: use CMAKE_CURRENT_LIST_DIR to find FPHSA

The version of CMake required to build CMake is now new enough to have
that variable.

Modules/FindLibArchive.cmake

@@ -48,10 +48,7 @@ endif()
 
 # Handle the QUIETLY and REQUIRED arguments and set LIBARCHIVE_FOUND
 # to TRUE if all listed variables are TRUE.
-# (Use ${CMAKE_ROOT}/Modules instead of ${CMAKE_CURRENT_LIST_DIR} because CMake
-#  itself includes this FindLibArchive when built with an older CMake that does
-#  not provide it.  The older CMake also does not have CMAKE_CURRENT_LIST_DIR.)
-include(${CMAKE_ROOT}/Modules/FindPackageHandleStandardArgs.cmake)
+include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
 find_package_handle_standard_args(LibArchive
                                   REQUIRED_VARS LibArchive_LIBRARY LibArchive_INCLUDE_DIR
                                   VERSION_VAR LibArchive_VERSION