cmt: update to 1.18 and make it buildable

[meator]

The 1.17 version doesn't build:

=> xbps-src: updating repositories for host (x86_64)...
[*] Updating repository `https://repo-default.voidlinux.org/current/x86_64-repodata' ...
[*] Updating repository `https://repo-default.voidlinux.org/current/nonfree/x86_64-repodata' ...
[*] Updating repository `https://repo-default.voidlinux.org/current/debug/x86_64-repodata' ...
[*] Updating repository `https://repo-default.voidlinux.org/current/multilib/x86_64-repodata' ...
[*] Updating repository `https://repo-default.voidlinux.org/current/multilib/nonfree/x86_64-repodata' ...
=> xbps-src: updating software in / masterdir...
=> xbps-src: cleaning up / masterdir...
=> cmt-1.17_2: removing autodeps, please wait...
=> cmt-1.17_2: building [gnu-makefile] for x86_64...
   [target] ladspa-sdk-1.15_3: found (https://repo-default.voidlinux.org/current)
=> cmt-1.17_2: installing target dependencies: ladspa-sdk-1.15_3 ...
=> cmt-1.17_2: running do-fetch hook: 00-distfiles ...
=> cmt-1.17_2: fetching distfile 'cmt_1.17.tgz' from 'http://www.ladspa.org/download/cmt_1.17.tgz'...
http://www.ladspa.org/download/cmt_1.17.tgz: Not Found
=> ERROR: cmt-1.17_2: failed to fetch 'cmt_1.17.tgz'.

Testing the changes

• I tested the changes in this PR: NO