Add POSIX binary tree search API.

* mingwex/tfind.c: New file.
	* mingwex/tdelete.c: New file.
	* mingwex/tsearch.c: New file.
	* mingwex/twalk.c: New file.
	* mingwex/Makefile.in (DISTFILES): Add tsearch.c twalk.c tdelete.c tfind.c.
	* mingwex/Makefile.in (POSIX_OBJS): Add tsearch.o twalk.o tdelete.o tfind.o.
	* include/search.h (tfind): Declare.
	(tdelete): Declare.
	(tsearch): Declare.
	(twalk): Declare.
	(ENTRY): Define.
	(ACTION): Define.
	(VISIT): Define.
	(node_t): Define, on condition of _SEARCH_PRIVATE.

winsup/mingw/mingwex/twalk.c

@@ -0,0 +1,48 @@
+/*	$NetBSD: twalk.c,v 1.2 1999/09/16 11:45:37 lukem Exp $	*/
+
+/*
+ * Tree search generalized from Knuth (6.2.2) Algorithm T just like
+ * the AT&T man page says.
+ *
+ * The node_t structure is for internal use only, lint doesn't grok it.
+ *
+ * Written by reading the System V Interface Definition, not the code.
+ *
+ * Totally public domain.
+ */
+
+#include <assert.h>
+#define _SEARCH_PRIVATE
+#include <search.h>
+#include <stdlib.h>
+
+static void trecurse (const node_t *, void (*action)(const void *, VISIT, int),
+	              int level)  __MINGW_ATTRIB_NONNULL (1)
+				  __MINGW_ATTRIB_NONNULL (2);
+/* Walk the nodes of a tree */
+static void
+trecurse( const node_t *root,	/* Root of the tree to be walked */
+	void (*action)(const void *, VISIT, int),
+	int level)
+{
+	if (root->llink == NULL && root->rlink == NULL)
+		(*action)(root, leaf, level);
+	else {
+		(*action)(root, preorder, level);
+		if (root->llink != NULL)
+			trecurse(root->llink, action, level + 1);
+		(*action)(root, postorder, level);
+		if (root->rlink != NULL)
+			trecurse(root->rlink, action, level + 1);
+		(*action)(root, endorder, level);
+	}
+}
+
+/* Walk the nodes of a tree */
+void
+twalk( const void *vroot,	/* Root of the tree to be walked */
+	void (*action) (const void *, VISIT, int))
+{
+	if (vroot != NULL && action != NULL)
+		trecurse(vroot, action, 0);
+}