Fix building virglrenderer in-tree for AOSP
This MR collects some preparatory changes to build virglrenderer in-tree for Android, with the goal of using the latest upstream virglrenderer code in external/virglrenderer
in an AOSP tree.
Some of the changes are inspired by the AOSP fork of virglrenderer at https://android.googlesource.com/platform/external/virglrenderer/
This MR does not add an Android.bp
file, as discussion is still on-going on whether it's better to have that in AOSP only to avoid bit-rotting.
Edited by Antonio Ospite