glx/dri3: Provide error diagnostics when DRI3 allocation fails

glx/dri3: Provide error diagnostics when DRI3 allocation fails

Instead of just segfaulting in the driver when a buffer allocation fails,
report error messages indicating what went wrong so that we can debug things.

As a simple example, chromium wraps Mesa in a sandbox which doesn't allow
access to most syscalls, including the ability to create shared memory
segments for fences. Before, you'd get a simple segfault in mesa and your 3D
acceleration would fail. Now you get:

$ chromium --disable-gpu-blacklist
[10618:10643:0930/200525:ERROR:nss_util.cc(856)] After loading Root Certs, loaded==false: NSS error code: -8018
libGL: pci id for fd 12: 8086:0a16, driver i965
libGL: OpenDriver: trying /local-miki/src/mesa/mesa/lib/i965_dri.so
libGL: Can't open configuration file /home/keithp/.drirc: Operation not permitted.
libGL: Can't open configuration file /home/keithp/.drirc: Operation not permitted.
libGL error: DRI3 Fence object allocation failure Operation not permitted
[10618:10618:0930/200525:ERROR:command_buffer_proxy_impl.cc(153)] Could not send GpuCommandBufferMsg_Initialize.
[10618:10618:0930/200525:ERROR:webgraphicscontext3d_command_buffer_impl.cc(236)] CommandBufferProxy::Initialize failed.
[10618:10618:0930/200525:ERROR:webgraphicscontext3d_command_buffer_impl.cc(256)] Failed to initialize command buffer.

This made it pretty easy to diagnose the problem in the referenced bug report.

Bugzilla: https://code.google.com/p/chromium/issues/detail?id=415681
Signed-off-by: Keith Packard <keithp@keithp.com>
Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Matt Turner <mattst88@gmail.com>