missing/explicit_bzero.c: Fixup r52806

Maybe kosaki had a better version, but CI failure emails are
annoying.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52819 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Tue Dec  1 07:50:33 2015  Eric Wong  <e@80x24.org>
+
+	* missing/explicit_bzero.c: new file. define explicit_bzero.
+	  Fixup r52806
+
 Thu Oct 22 12:54:43 2015  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* thread_pthread.c (register_ubf_list): renamed from
@@ -88,7 +93,6 @@ Wed Oct 21 08:23:36 2015  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 Sun Oct 18 17:26:53 2015  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
-	* missing/explicit_bzero.c: new file. define explicit_bzero.
 	* common.mk: add a rule for explicit.o.
 	* configure.in: detect explicit_bzero and memset_s.
 	* include/ruby/missing.h: add explicit_bzero.

missing/explicit_bzero.c

@@ -0,0 +1,8 @@
+#include <string.h>
+
+/* prevent the compiler from optimizing away memset or bzero */
+void
+explicit_bzero(void *p, size_t n)
+{
+    memset(p, 0, n);
+}