don't set the -rpath/-L flags to the install dir as this breaks DESTDIR

--- a/SConstruct
+++ b/SConstruct
@@ -268,11 +268,7 @@
     return wrapped
 
 # Honor the specified installation prefix in link paths.
-if not env["sysroot"]:
-    env.Prepend(LIBPATH=[installdir('libdir')])
-else:
-    env.Prepend(LIBPATH=[env["sysroot"] + installdir('libdir')])
-if env["shared"]:
+if env["shared"] and env["chrpath"]:
     env.Prepend(RPATH=[installdir('libdir')])
 
 # Give deheader a way to set compiler flags