tgsi: try and handle overflowing shaders. (v2)

tgsi: try and handle overflowing shaders. (v2)

This is used to detect error in virgl if we overflow the shader
dumping buffers.

v2: return a bool.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>