[Mesa-dev] prep work for 64-bit integer support

[Dave Airlie]

While writing ARB_gpu_shader_int64 I realised I needed to change
a lot of existing checks for doubles to 64bit, so I decided to
do that as much in advance as possible.

This adds a macro + interface to check if a type is 64-bit,
which currently is only true for doubles, it then uses the new
API in places where it makes sense.

There is also a patch to st/glsl_to_tgsi to use glsl_base_type
enum for better type safety.

Dave.