cmake: Call get_filename_component() with DIRECTORY mode instead of PATH mode (#9614)

PATH mode is legacy alias for DIRECTORY mode (needed only for CMake <= 2.8.11):
https://cmake.org/cmake/help/latest/command/get_filename_component.html

cmake/install.cmake

@@ -51,7 +51,7 @@ foreach(_extract_string ${_extract_strings})
   string(REPLACE "\\" "/" _header ${_header})
   get_filename_component(_extract_from "${protobuf_SOURCE_DIR}/src/${_header}" ABSOLUTE)
   get_filename_component(_extract_name ${_header} NAME)
-  get_filename_component(_extract_to "${CMAKE_INSTALL_INCLUDEDIR}/${_header}" PATH)
+  get_filename_component(_extract_to "${CMAKE_INSTALL_INCLUDEDIR}/${_header}" DIRECTORY)
   if(EXISTS "${_extract_from}")
     install(FILES "${_extract_from}"
       DESTINATION "${_extract_to}"
@@ -88,10 +88,10 @@ _protobuf_auto_list("${protobuf_SOURCE_DIR}/src/Makefile.am" nobase_dist_proto_D
 foreach(_file ${nobase_dist_proto_DATA})
   get_filename_component(_file_from "${protobuf_SOURCE_DIR}/src/${_file}" ABSOLUTE)
   get_filename_component(_file_name ${_file} NAME)
-  get_filename_component(_file_path ${_file} PATH)
+  get_filename_component(_dir ${_file} DIRECTORY)
   if(EXISTS "${_file_from}")
     install(FILES "${_file_from}"
-      DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/${_file_path}"
+      DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/${_dir}"
       COMPONENT protobuf-protos
       RENAME "${_file_name}")
   else()

cmake/protobuf-config.cmake.in

@@ -84,10 +84,10 @@ function(protobuf_generate)
     # Create an include path for each file specified
     foreach(_file ${protobuf_generate_PROTOS})
       get_filename_component(_abs_file ${_file} ABSOLUTE)
-      get_filename_component(_abs_path ${_abs_file} PATH)
-      list(FIND _protobuf_include_path ${_abs_path} _contains_already)
+      get_filename_component(_abs_dir ${_abs_file} DIRECTORY)
+      list(FIND _protobuf_include_path ${_abs_dir} _contains_already)
       if(${_contains_already} EQUAL -1)
-          list(APPEND _protobuf_include_path -I ${_abs_path})
+          list(APPEND _protobuf_include_path -I ${_abs_dir})
       endif()
     endforeach()
   endif()

cmake/tests.cmake

@@ -92,7 +92,7 @@ set(tests_protos
 )
 
 macro(compile_proto_file filename)
-  get_filename_component(dirname ${filename} PATH)
+  get_filename_component(dirname ${filename} DIRECTORY)
   get_filename_component(basename ${filename} NAME_WE)
   add_custom_command(
     OUTPUT ${protobuf_SOURCE_DIR}/src/${dirname}/${basename}.pb.cc