autoconf: Add support for shared DRI build on linux and freebsd

Added autoconf bits to allow using DRI as the driver through the option
--with-dri-driver=DRIVER. The options are x11 (default) and dri. Three
DRI specific options for controlling the driver directory, direct
rendering and TLS are also added.

The DRI will probably not work for platforms besides linux and freebsd.
2 files changed