New comment by tornaria on void-packages repository

https://github.com/void-linux/void-packages/pull/30032#issuecomment-894868859

Comment:
> My `_GNU_SOURCE` suggestion was apparently a bad idea for one of the packages, feel free to move it back to a conditional for musl.

I actually went ahead and fixed it at the source: https://github.com/wbhart/flint2/pull/988 and https://github.com/fredrik-johansson/arb/pull/376. My new version will include those as patches which they will hopefully be merged upstream.