Enable the RPATH always (key4hep#4)

Co-authored-by: jmcarcell <[email protected]>

CMakeLists.txt

@@ -26,6 +26,25 @@ if(NOT CMAKE_CXX_STANDARD MATCHES "14|17|20")
   message(FATAL_ERROR "Unsupported C++ standard: ${CMAKE_CXX_STANDARD}")
 endif()
 
+# use, i.e. don't skip the full RPATH for the build tree
+set(CMAKE_SKIP_BUILD_RPATH FALSE)
+
+# when building, don't use the install RPATH already
+# (but later on when installing)
+set(CMAKE_BUILD_WITH_INSTALL_RPATH FALSE)
+
+set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")
+
+# add the automatically determined parts of the RPATH
+# which point to directories outside the build tree to the install RPATH
+set(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)
+
+# the RPATH to be used when installing, but only if it's not a system directory
+list(FIND CMAKE_PLATFORM_IMPLICIT_LINK_DIRECTORIES "${CMAKE_INSTALL_PREFIX}/lib" isSystemDir)
+if("${isSystemDir}" STREQUAL "-1")
+    set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")
+endif("${isSystemDir}" STREQUAL "-1")
+
 include(CTest)
 
 add_subdirectory(DCHdigi)