Fix ICD generation (again).
Fix ICD generation (again).

The correct usage is to use root_out_dir in the output file name
and to use root_build_dir in the rebased arguments.

Fixes the 32-bit NACL build on Windows. (Tested locally)

Bug: dawn:283
Change-Id: I1d6ca062306a4662eef5c922296e9c95fb047acd
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38828
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Tested-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Presubmit-Ready: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>
Kokoro-Presubmit: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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