Support pkg-config

Let's add pkg-config and install headers since this is needed for
ozone to build with a gbm platform.

BUG=chromium:394868,chromium:402597,chromium:413947,chromium:412508
TEST=emerge minigbm, then try pkg-config-board --libs --cflags. Rejoice that it works!

Change-Id: I94a26b1986db76e2d0dad638feda80ec10f48a9f
Reviewed-on: https://chromium-review.googlesource.com/218979
Reviewed-by: Stéphane Marchesin <[email protected]>
Tested-by: Stéphane Marchesin <[email protected]>
2 files changed