Fix broken DIR_LIBRARY usages (#764)

In the commit a13ed0a (PR #763), some DIR_LIBRARY variable usages are modified to make install destination relative to be more portable, but this will break the original designed purpose of DIR_LIBRARY, so this commit will revert the changes.

Author: WhiredPlanck

CMakeLists.txt

@@ -131,15 +131,15 @@ write_basic_package_version_file(
 configure_package_config_file(
   OpenCCConfig.cmake.in
   ${CMAKE_CURRENT_BINARY_DIR}/OpenCCConfig.cmake
-  INSTALL_DESTINATION lib/cmake/opencc
+  INSTALL_DESTINATION ${DIR_LIBRARY}/cmake/opencc
 )
 
 install(
   FILES
     ${CMAKE_CURRENT_BINARY_DIR}/OpenCCConfig.cmake
     ${CMAKE_CURRENT_BINARY_DIR}/OpenCCConfigVersion.cmake
   DESTINATION
-    lib/cmake/opencc
+    ${DIR_LIBRARY}/cmake/opencc
 )
 
 ######## Compiler flags

src/CMakeLists.txt

@@ -150,15 +150,15 @@ endif()
 
 install(
   TARGETS ${INSTALL_TARGETS} EXPORT ${targets_export_name}
-  LIBRARY DESTINATION lib
-  ARCHIVE DESTINATION lib
+  LIBRARY DESTINATION ${DIR_LIBRARY}
+  ARCHIVE DESTINATION ${DIR_LIBRARY}
   RUNTIME DESTINATION bin
 )
 
 install(
   EXPORT ${targets_export_name}
   FILE ${targets_export_name}.cmake
-  DESTINATION lib/cmake/opencc
+  DESTINATION ${DIR_LIBRARY}/cmake/opencc
   NAMESPACE OpenCC::
 )