Fix the cmake configuration file install path to be more standards compliant…

Fix the cmake configuration file install path to be more standards compliant (See the description of cmake's config search behavior on https://cmake.org/cmake/help/v3.4/command/find_package.html)

cmake/install.cmake

@@ -83,9 +83,15 @@ foreach(_file ${nobase_dist_proto_DATA})
 endforeach()
 
 # Export configuration
+set(_cmakedir_desc "Directory relative to CMAKE_INSTALL to install the cmake configuration files")
+if(NOT MSVC)
+  set(CMAKE_INSTALL_CMAKEDIR "${CMAKE_INSTALL_LIBDIR}/cmake/protobuf" CACHE STRING "${_cmakedir_desc")
+else()
+  set(CMAKE_INSTALL_CMAKEDIR "cmake" CACHE STRING "${_cmakedir_desc}")
+endif()
 
 install(EXPORT protobuf-targets
-  DESTINATION "lib/cmake/protobuf"
+  DESTINATION "${CMAKE_INSTALL_CMAKEDIR}"
   COMPONENT protobuf-export)
 
 configure_file(protobuf-config.cmake.in
@@ -99,5 +105,5 @@ install(FILES
   "${protobuf_BINARY_DIR}/protobuf-config.cmake"
   "${protobuf_BINARY_DIR}/protobuf-config-version.cmake"
   "${protobuf_BINARY_DIR}/protobuf-module.cmake"
-  DESTINATION "lib/cmake/protobuf"
+  DESTINATION "${CMAKE_INSTALL_CMAKEDIR}"
   COMPONENT protobuf-export)