Fix Subzero's LLVM bitcode reader to use a diagnostic handler.
Fix Subzero's LLVM bitcode reader to use a diagnostic handler.

This encorporate the changes introduced by llvm CL
https://codereview.chromium.org/1310883003 (see for details).

BUG=None
R=dschuff@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/1312473006 .

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