[Truffle] Add File.symlink POSIX node.

Author: bjfish

spec/truffle/tags/core/file/symlink_tags.txt

@@ -1,6 +1,2 @@
 fails:File.symlink creates a symlink between a source and target file
-fails:File.symlink creates a symbolic link
-fails:File.symlink accepts args that have #to_path methods
 fails:File.symlink raises an Errno::EEXIST if the target already exists
-fails:File.symlink? returns true if the file is a link
-fails:File.symlink? accepts an object that has a #to_path method

truffle/src/main/java/org/jruby/truffle/nodes/rubinius/PosixNodes.java

@@ -318,4 +318,22 @@ public int isATTY(int fd) {
 
     }
 
+    @CoreMethod(names = "symlink", isModuleFunction = true, required = 2)
+    public abstract static class SymlinkNode extends CoreMethodNode {
+
+        public SymlinkNode(RubyContext context, SourceSection sourceSection) {
+            super(context, sourceSection);
+        }
+
+        public SymlinkNode(SymlinkNode prev) {
+            super(prev);
+        }
+
+        @Specialization
+        public int symlink(RubyString first, RubyString second) {
+            return posix().symlink(first.toString(), second.toString());
+        }
+
+    }
+
 }