Accumulate compile-time constant and runtime offsets separately
Accumulate compile-time constant and runtime offsets separately

This makes WalkAccessChain slightly easier on the backend -- there is
less constant folding to do.

Bug: b/124388146

Change-Id: I4e76c3e494278e1399b8a86134b652c2a6d96d8c
Reviewed-on: https://swiftshader-review.googlesource.com/c/24988
Tested-by: Chris Forbes <c3279c50043e18e9442c1ae071cafa0e7a4ca967@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader