add asprintf / vasprintf from OpenSSH portable

ok deraadt@ beck@

include/Makefile.am

@@ -2,6 +2,7 @@ SUBDIRS = openssl
 
 noinst_HEADERS = err.h
 noinst_HEADERS += pqueue.h
+noinst_HEADERS += stdio.h
 noinst_HEADERS += stdlib.h
 noinst_HEADERS += string.h
 noinst_HEADERS += unistd.h

include/stdio.h

@@ -0,0 +1,11 @@
+#include_next <stdio.h>
+
+#ifndef LIBCRYPTOCOMPAT_STDIO_H
+#define LIBCRYPTOCOMPAT_STDIO_H
+
+#ifdef NO_ASPRINTF
+int vasprintf(char **str, const char *fmt, va_list ap);
+int asprintf(char **str, const char *fmt, ...);
+#endif
+
+#endif