build: fix problems with "struct stat" not being defined under eCos

Include <sys/stat.h> according to
http://www.opengroup.org/onlinepubs/000095399/functions/stat.html

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

src/target/arm_semihosting.c

@@ -43,6 +43,7 @@
 #include "arm_semihosting.h"
 #include <helper/binarybuffer.h>
 #include <helper/log.h>
+#include <sys/stat.h>
 
 static int open_modeflags[12] = {
 	O_RDONLY,