The 'builtins' scope was rather specific to the initial SPIR-V SSA debugging functionality, and doesn't really fit with the rich debug model.
Just replace it with a more sensible globals scope.

Fixes issues where these globals were only visible in the initial stack frame.

Bug: b/148401179
Change-Id: Id229e891edb8ece3694d989b48d3399d5d489d47
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/45356Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>