Document several older QEMU vulnerabilities

Security: CVE-2015-3214
Security: CVE-2015-5158
Security: CVE-2015-5225
Security: CVE-2015-5745
Security: https://vuxml.FreeBSD.org/freebsd/2b3b4c27-b0c7-11e5-8d13-bc5ff45d0f28.html
Security: https://vuxml.FreeBSD.org/freebsd/21e5abe3-b0c6-11e5-8d13-bc5ff45d0f28.html
Security: https://vuxml.FreeBSD.org/freebsd/a267cd6c-b0c4-11e5-8d13-bc5ff45d0f28.html
Security: https://vuxml.FreeBSD.org/freebsd/aea8d90e-b0c1-11e5-8d13-bc5ff45d0f28.html