make more directories configurable

CMakeLists.txt

@@ -19,12 +19,16 @@ endif()
 
 message(STATUS MONERO_DIR ": ${MONERO_DIR}")
 
+if (NOT MONERO_SOURCE_DIR)
     set(MONERO_SOURCE_DIR ${MONERO_DIR}
           CACHE PATH "Path to the root directory for Monero")
+endif()
 
+if (NOT MONERO_BUILD_DIR)
     # set location of monero build tree
     set(MONERO_BUILD_DIR ${MONERO_SOURCE_DIR}/build/release/
           CACHE PATH "Path to the build directory for Monero")
+endif()
 
 set(MY_CMAKE_DIR "${CMAKE_CURRENT_LIST_DIR}/cmake"
         CACHE PATH "The path to the cmake directory of the current project")