mariadb: fix floating dependency on krb5

Mariadb depends on openssl, openssl conditionally depends on krb5 by
checking if OPENSSL_NO_KRB5 is defined, but cmake can not handle "ifndef"
and always ask krb5.h if krb5.h exist when cmake make_depend;

Faking a kssl.h if krb5 is not in PACKAGECONF, which does not include
krb5 related declaration, install the faked kssl.h into build dir to
be searched firstly

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>