This can be #defined in the assembly files, reducing per-build-system complexity.

Bug: b/139010488
Change-Id: Ided03000dc5e93e4d1e04ce6f0b57c6e45565545
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/35210
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>