Add compat strdupa() implementation from libnostd

This patch adds compat support, to *BSD and other UNIX, for GLIBC
strdupa() function, used in mkpath().  The implementation is taken
from http://www.25thandclement.com/~william/projects/libnostd.html
by William Ahern.

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

strlite.h

@@ -25,6 +25,7 @@
 #define LITE_STRING_H_
 
 #include <string.h>
+#include "strdupa.h"
 
 #ifndef strlcpy
 size_t  strlcpy    (char *dst, const char *src, size_t siz);