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

mesa: update to 20.1.4, fix patches
https://github.com/void-linux/void-packages/pull/23499

Description:
`fix-libXvMC-versioning.patch` was fixed upstream [here](https://github.com/mesa3d/mesa/commit/a35c4675a72c30e6b7e116237a43ca7c520b060d).
For `clover-ppc64-cpp14.patch`, the `clover_cpp_std` variable was removed completely, so not sure if that still works.