cache install prefix

src/lowtran/cmake/options.cmake

@@ -1,17 +1,10 @@
 include(GNUInstallDirs)
 
-# Rpath options necessary for shared library install to work correctly in user projects
-set(CMAKE_INSTALL_NAME_DIR ${CMAKE_INSTALL_FULL_LIBDIR})
-set(CMAKE_INSTALL_RPATH ${CMAKE_INSTALL_FULL_LIBDIR})
-set(CMAKE_INSTALL_RPATH_USE_LINK_PATH true)
-
 # Necessary for shared library with Visual Studio / Windows oneAPI
 set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS true)
 
-if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
-  # will not take effect without FORCE
-  # CMAKE_BINARY_DIR for use from FetchContent
-  set(CMAKE_INSTALL_PREFIX ${CMAKE_BINARY_DIR} CACHE PATH "Install top-level directory" FORCE)
+if(PROJECT_IS_TOP_LEVEL AND CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+  set_property(CACHE CMAKE_INSTALL_PREFIX PROPERTY VALUE "${PROJECT_BINARY_DIR}")
 endif()
 
 file(GENERATE OUTPUT .gitignore CONTENT "*")