FindGDAL: conditionally set the output variables

Modules/FindGDAL.cmake

@@ -160,12 +160,14 @@ FIND_PACKAGE_HANDLE_STANDARD_ARGS(GDAL
     VERSION_VAR GDAL_VERSION
     REQUIRED_VARS GDAL_LIBRARY GDAL_INCLUDE_DIR)
 
-if (GDAL_FOUND AND NOT TARGET GDAL::GDAL)
-    add_library(GDAL::GDAL UNKNOWN IMPORTED)
-    set_target_properties(GDAL::GDAL PROPERTIES
-        IMPORTED_LOCATION "${GDAL_LIBRARY}"
-        INTERFACE_INCLUDE_DIRECTORIES "${GDAL_INCLUDE_DIR}")
+if (GDAL_FOUND)
+    set(GDAL_LIBRARIES ${GDAL_LIBRARY})
+    set(GDAL_INCLUDE_DIRS ${GDAL_INCLUDE_DIR})
+
+    if (NOT TARGET GDAL::GDAL)
+        add_library(GDAL::GDAL UNKNOWN IMPORTED)
+        set_target_properties(GDAL::GDAL PROPERTIES
+            IMPORTED_LOCATION "${GDAL_LIBRARY}"
+            INTERFACE_INCLUDE_DIRECTORIES "${GDAL_INCLUDE_DIR}")
+    endif ()
 endif ()
-
-set(GDAL_LIBRARIES ${GDAL_LIBRARY})
-set(GDAL_INCLUDE_DIRS ${GDAL_INCLUDE_DIR})