Clean build environments can't download kernel source

[buzzer13]

Clean build environments can't download kernel source, probably because of kernel.org ftp service termination, as mentioned here:

​https://kernel.org/shutting-down-ftp-services.html

Also there are no sources on openwrt mirrors.
Here is the part of the log:

HTTP request sent, awaiting response... failed: Name or service not known.
wget: unable to resolve host address 'ftp.all.kernel.org'
connected.
Download failed.
connected.
--2017-03-02 22:18:01--  http://ftp.all.kernel.org/pub/linux/kernel/v3.x/linux-3.18.45.tar.xz
Resolving ftp.all.kernel.org (ftp.all.kernel.org)... failed: Name or service not known.
wget: unable to resolve host address 'ftp.all.kernel.org'
Download failed.
--2017-03-02 22:18:01--  ftp://ftp.all.kernel.org/pub/linux/kernel/v3.x/longterm/v3.18.45/linux-3.18.45.tar.xz
Resolving ftp.all.kernel.org (ftp.all.kernel.org)... failed: Name or service not known.
wget: unable to resolve host address 'ftp.all.kernel.org'
Download failed.
--2017-03-02 22:18:02--  http://ftp.all.kernel.org/pub/linux/kernel/v3.x/longterm/v3.18.45/linux-3.18.45.tar.xz
Resolving ftp.all.kernel.org (ftp.all.kernel.org)... failed: Name or service not known.
wget: unable to resolve host address 'ftp.all.kernel.org'
Download failed.
--2017-03-02 22:18:02--  http://mirror2.openwrt.org/sources/linux-3.18.45.tar.xz
Resolving mirror2.openwrt.org (mirror2.openwrt.org)... 46.4.11.11
Connecting to mirror2.openwrt.org (mirror2.openwrt.org)|46.4.11.11|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
2017-03-02 22:18:02 ERROR 404: Not Found.
Download failed.
--2017-03-02 22:18:02--  http://downloads.openwrt.org/sources/linux-3.18.45.tar.xz
Resolving downloads.openwrt.org (downloads.openwrt.org)... 78.24.191.177
Connecting to downloads.openwrt.org (downloads.openwrt.org)|78.24.191.177|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
2017-03-02 22:18:02 ERROR 404: Not Found.

Download failed.
No more mirrors to try - giving up.
Makefile:100: recipe for target '/builds/buzzer13/openwrt-builds/src/chaos_calmer/dl/linux-3.18.45.tar.xz' failed

[buzzer13]

Fix mirrors list