SuperBuild: remove dups from cmake_install_prefix

SuperBuild/CMakeLists.txt

@@ -128,6 +128,8 @@ else()
   set(SB_CMAKE_PREFIX_PATH "${SB_INSTALL_PREFIX}")
 endif()
 
+list(REMOVE_DUPLICATES SB_CMAKE_PREFIX_PATH)
+
 set(SB_CMAKE_CACHE_ARGS)
 list(APPEND SB_CMAKE_CACHE_ARGS "-DCMAKE_BUILD_TYPE:STRING=${CMAKE_BUILD_TYPE}")
 list(APPEND SB_CMAKE_CACHE_ARGS "-DCMAKE_INSTALL_PREFIX:PATH=${SB_INSTALL_PREFIX}")