Add compat strndupa() implementation from libnostd

This patch adds compat support, to *BSD and other UNIX, for the GLIBC
strndupa() function.  The implementation is taken from libnostd written
by William Ahern.

http://www.25thandclement.com/~william/projects/libnostd.html

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

strlite.h

@@ -26,6 +26,7 @@
 
 #include <string.h>
 #include "strdupa.h"
+#include "strndupa.h"
 
 #ifndef strlcpy
 size_t  strlcpy    (char *dst, const char *src, size_t siz);

strndupa.h

@@ -0,0 +1,56 @@
+/* ==========================================================================
+ * strndupa.h - Re-implementation of glibc strndupa.
+ * --------------------------------------------------------------------------
+ * Copyright (c) 2009  William Ahern
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to permit
+ * persons to whom the Software is furnished to do so, subject to the
+ * following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+ * NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+ * USE OR OTHER DEALINGS IN THE SOFTWARE.
+ * ==========================================================================
+ */
+#ifndef GNU_STRING_STRNDUPA_H
+#define GNU_STRING_STRNDUPA_H
+
+
+#if !defined(HAVE_STRNDUPA)
+#if defined(strndupa)
+#define HAVE_STRNDUPA	1
+#endif
+#endif
+
+
+#if !HAVE_STRNDUPA
+#if defined(__GNUC__)
+#include <stddef.h>	/* size_t */
+
+#include <string.h>	/* memcpy(3) */
+
+#include <gnu/string/strnlen.h>
+
+#define strndupa(src, lim) (__extension__ ({		\
+	size_t len_	= strnlen(src, lim);		\
+	char *dst_	= __builtin_alloca(len_ + 1);	\
+	dst_[len_]	= '\0';				\
+	(char *)memcpy(dst_, src, len_);		\
+}))
+
+#endif /* __GNUC__ */
+#endif /* !HAVE_STRNDUPA */
+
+
+#endif /* GNU_STRING_STRNDUPA_H */