There is an updated pull request by jnbr against master on the void-packages repository

https://github.com/jnbr/void-packages icecat
https://github.com/void-linux/void-packages/pull/15221

icecat: fix build
- the vendored version of cssparser fails to build with current rust
- glibc-2.30 introduced gettid as a function

A patch file from https://github.com/void-linux/void-packages/pull/15221.patch is attached