automake: Link all libGL.so variants with -Bsymbolic.

automake: Link all libGL.so variants with -Bsymbolic.

We were linking src/glx with -Bsymbolic, but not the classic/gallium X11
libGL.so.

But it's always a good idea to build all libGL.so and all DRI drivers
with -Bsymbolic, otherwise they might resolve symbols from the 3rd party
application executable or shared libraries, which is _never_ what we
want.

In particular, this can happen when intercepting OpenGL calls with
apitrace, before
https://github.com/apitrace/apitrace/commit/63194b2573176ef34efce1a5c8b08e624b8dddf5

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>