wchar.h: improve wchar_t support in Bionic

Change-Id: Iffd41046fd0933c66542abf7627a1569522dfcb2
diff --git a/libc/wchar/wcsxfrm.c b/libc/wchar/wcsxfrm.c
new file mode 100644
index 0000000..042ea56
--- /dev/null
+++ b/libc/wchar/wcsxfrm.c
@@ -0,0 +1,57 @@
+/*-
+ * Copyright (c) 1995 Alex Tatmanjants <alex@elvisti.kiev.ua>
+ *		at Electronni Visti IA, Kiev, Ukraine.
+ *			All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <wchar.h>
+
+/*
+ * Placeholder wcsxfrm() implementation. See wcscoll.c for a description of
+ * the logic used.
+ */
+size_t
+wcsxfrm(wchar_t * __restrict dest, const wchar_t * __restrict src, size_t len)
+{
+    int prim, sec, l;
+    size_t slen;
+    char *mbsrc, *s, *ss;
+
+    if (*src == L'\0') {
+        if (len != 0)
+            *dest = L'\0';
+        return (0);
+    }
+
+    slen = wcslen(src);
+    if (len > 0) {
+        if (slen < len)
+            wcscpy(dest, src);
+        else {
+            wcsncpy(dest, src, len - 1);
+            dest[len - 1] = L'\0';
+        }
+    }
+    return (slen);
+}