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

ghc: add build option "bindist"
https://github.com/void-linux/void-packages/pull/20368

Description:
Setting the `bindist` option adapts the template to not only build
`ghc`, without using the system libffi, but also create a binary
distribution and install it in the source distfiles folder:
`${XBPS_SRCDISTDIR}/ghc-${version}-void-linux-${XBPS_TARGET_LIBC}.tar.xz`

Perhaps this can be incorporated in #20365