There is a new pull request by oynqr against master on the void-packages repository

https://github.com/oynqr/void-packages arc-theme
https://github.com/void-linux/void-packages/pull/31090

arc-theme: update to 20210412.
<!-- Mark items with [x] where applicable -->

#### General
- [ ] This is a new package and it conforms to the [quality requirements](https://github.com/void-linux/void-packages/blob/master/Manual.md#quality-requirements)

#### Have the results of the proposed changes been tested?
- [x] I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
- [ ] I generally don't use the affected packages but briefly tested this PR

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Upstream switched to meson and dropped the use of optipng.

A patch file from https://github.com/void-linux/void-packages/pull/31090.patch is attached