There's a closed pull request on the void-packages repository

libsigc++: update to 2.12.0.
https://github.com/void-linux/void-packages/pull/41241

Description:
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#### Testing the changes
- I tested the changes in this PR: **briefly** (compiled and ran Waybar, which depends on libsigc++, but I couldn't for the life of me compile a simple example program to test libsigc++ directly)

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