Added flag --enable-vgl mapped to HAVE_VCL_OPEN_GL_BACKEND

Change-Id: I8077d90ecb950740ce76a37444658d8bdc799453
make works with OpenGLSalInstance / OpenGLSalGraphics

Change-Id: Ie5156dd15122586e9c173a3532759a3be728809a
change return type to ImplFontCharMapPtr post creating vcl-opengl2 branch

Change-Id: Id2022cf1b3665b54356c28deda51d82e172a839e