MesaLib: various changes to how this is built

- Try to appease the Darwin build.
- Simplify and reduce the number of options to make testing easier.
- Silence lots of pkglint warnings.
- Enable the surfaceless platform as recommended by Mesa.
- Switch to gallium swrast as recommended by Mesa.
- Switch to gallium osmesa as recommended by Mesa.
- Support building without X11.

todo:
- glvnd support (needs testing to figure out which platforms it builds on)
- make AMD drivers optional on platforms like aarch64

Bump PKGREVISION.

(nia)