Build libchartopengl for all platforms

That doesn't mean it would need to be used on iOS or Android, if we
don't need/want to.

Change-Id: Ia6ac6f32cac3f6958f5ec240ec4be369474edfb8
Add gluErrorString() replacement to OpenGLHelper

Change-Id: I1a04ece7026ceff75456df03b4eb189a3cb9687f
Use OpenGLHelper::GLErrorString()

Change-Id: I45f627b20c4cfdd3048d7b1716af882ddd0d82b9