CMakeLists.txt: Don't use DATADIR before it's defined

CMakeLists.txt

@@ -83,18 +83,6 @@ if (MSVC)
     option(OPENMW_LTO_BUILD "Build OpenMW with Link-Time Optimization (Needs ~2GB of RAM)" OFF)
 endif()
 
-# Location of morrowind data files
-if (APPLE)
-    set(MORROWIND_DATA_FILES "./data" CACHE PATH "location of Morrowind data files")
-    set(OPENMW_RESOURCE_FILES "./resources" CACHE PATH "location of OpenMW resources files")
-elseif(UNIX)
-    set(MORROWIND_DATA_FILES "${DATADIR}/data" CACHE PATH "location of Morrowind data files")
-    set(OPENMW_RESOURCE_FILES "${DATADIR}/resources" CACHE PATH "location of OpenMW resources files")
-else()
-    set(MORROWIND_DATA_FILES "data" CACHE PATH "location of Morrowind data files")
-    set(OPENMW_RESOURCE_FILES "resources" CACHE PATH "location of OpenMW resources files")
-endif(APPLE)
-
 if (WIN32)
     option(USE_DEBUG_CONSOLE "whether a debug console should be enabled for debug builds, if false debug output is redirected to Visual Studio output" ON)
 endif()
@@ -436,6 +424,18 @@ IF(NOT WIN32 AND NOT APPLE)
     INSTALL(DIRECTORY DESTINATION "${DATADIR}/data" COMPONENT "Resources")
 ENDIF(NOT WIN32 AND NOT APPLE)
 
+# Location of morrowind data files
+if (APPLE)
+    set(MORROWIND_DATA_FILES "./data" CACHE PATH "location of Morrowind data files")
+    set(OPENMW_RESOURCE_FILES "./resources" CACHE PATH "location of OpenMW resources files")
+elseif(UNIX)
+    set(MORROWIND_DATA_FILES "${DATADIR}/data" CACHE PATH "location of Morrowind data files")
+    set(OPENMW_RESOURCE_FILES "${DATADIR}/resources" CACHE PATH "location of OpenMW resources files")
+else()
+    set(MORROWIND_DATA_FILES "data" CACHE PATH "location of Morrowind data files")
+    set(OPENMW_RESOURCE_FILES "resources" CACHE PATH "location of OpenMW resources files")
+endif(APPLE)
+
 if(WIN32)
     FILE(GLOB dll_files "${OpenMW_BINARY_DIR}/Release/*.dll")
     INSTALL(FILES ${dll_files} DESTINATION ".")