In my_MD5Final in mysys/md5.c, ctx is not properly zeroed as intended

This is a copy of upstream http://bugs.mysql.com/bug.php?id=68909 for 5.1.

...
gcc -DDEFAULT_BASEDIR=\"/usr/local\" -DMYSQL_DATADIR="\"/usr/local/var\"" -DDEFAULT_CHARSET_HOME="\"/usr/local\"" -DSHAREDIR="\"/usr/local/share/mysql\"" -DDEFAULT_HOME_ENV=MYSQL_HOME -DDEFAULT_GROUP_SUFFIX_ENV=MYSQL_GROUP_SUFFIX -DDEFAULT_SYSCONFDIR="\"/usr/local/etc\"" -DHAVE_CONFIG_H -I. -I../include -I../include -I../include -I. -Wall -Wextra -Wunused -Wwrite-strings -Wno-strict-aliasing -Werror -Wdeclaration-after-statement -g -DSAFE_MUTEX -g -O2 -DUNIV_LINUX -DUNIV_LINUX -MT md5.o -MD -MP -MF .deps/md5.Tpo -c -o md5.o md5.c
md5.c: In function ‘my_MD5Final’:
md5.c:179:24: error: argument to ‘sizeof’ in ‘memset’ call is the same expression as the destination; did you mean to dereference it? [-Werror=sizeof-pointer-memaccess]
   memset(ctx, 0, sizeof(ctx)); /* In case it's sensitive */
                        ^