geotiff: add rpath entries to libraries

projects/geotiff.cmake

+set(geotiff_options)
+if (UNIX AND NOT APPLE)
+  list(APPEND geotiff_options
+    -DCMAKE_INSTALL_RPATH:STRING=<INSTALL_DIR>/lib)
+endif ()
+
 superbuild_add_project(geotiff
   DEPENDS tiff zlib proj
   LICENSE_FILES
@@ -7,7 +13,8 @@ superbuild_add_project(geotiff
     -DCMAKE_INSTALL_NAME_DIR:PATH=<INSTALL_DIR>/lib
     -DWITH_TIFF:BOOL=${tiff_enabled}
     -DWITH_ZLIB:BOOL=${zlib_enabled}
-    -DWITH_UTILITIES:BOOL=OFF)
+    -DWITH_UTILITIES:BOOL=OFF
+    ${geotiff_options})
 
 # GeoTIFF doesn't handle tiff's generated CMake package configuration well.
 # https://github.com/OSGeo/libgeotiff/issues/20