more robust: avoid global change of LD_LIBRARY_PATH (e.g. relevant for subprocesses);

--- a/src/Pure/ML/ml_process.scala	Fri Feb 09 17:42:15 2018 +0100
+++ b/src/Pure/ML/ml_process.scala	Fri Feb 09 17:57:36 2018 +0100
@@ -146,9 +146,7 @@
       "exec " + options.string("ML_process_policy") + """ "$ML_HOME/poly" -q """ +
         Bash.strings(bash_args),
       cwd = cwd,
-      env =
-        Isabelle_System.library_path(env ++ env_options ++ env_tmp,
-          Isabelle_System.getenv_strict("ML_HOME")),
+      env = env ++ env_options ++ env_tmp,
       redirect = redirect,
       cleanup = () =>
         {

--- a/src/Pure/System/isabelle_system.scala	Fri Feb 09 17:42:15 2018 +0100
+++ b/src/Pure/System/isabelle_system.scala	Fri Feb 09 17:57:36 2018 +0100
@@ -144,16 +144,6 @@
 
   def cygwin_root(): String = getenv_strict("CYGWIN_ROOT")
 
-  def library_path(env: Map[String, String], elem: String): Map[String, String] =
-    if (Platform.is_windows) env
-    else {
-      val x = if (Platform.is_macos) "DYLD_LIBRARY_PATH" else "LD_LIBRARY_PATH"
-      env.getOrElse(x, "") match {
-        case "" => env + (x -> elem)
-        case y => env + (x -> (y + ":" + elem))
-      }
-    }
-
 
 
   /** file-system operations **/