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

https://github.com/Johnnynator/void-packages gcc6
https://github.com/void-linux/void-packages/pull/43224

gcc6: update template to workaround file-prefix-map
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A patch file from https://github.com/void-linux/void-packages/pull/43224.patch is attached