[PATCH] Provide dri shared library building and SDK installation.

Patch cherry-picked from my dri-sdk-7.8 branch against current head (edb5253dfa). An earlier full build through of all drivers (except nouveau, i will play with its expansive libdrm dependencies later) showed it to be an exact match still.

This patch, while not harming or hampering anything or anyone, gives us the ability to maintain and build DRI drivers out of tree for those so inclined. Build system additions only. No adverse effects. Everybody wins.

I intend to provide changes as needed, I hope to at least manage to maintain released versions in the long term.

For those wanting a test run, please check out the 7.8 version of the SDK and the drivers in my cgit.freedesktop.org repos.

Luc Verhaegen.