Subzero: Add a missing absolute path to llvm-mc command.
Subzero: Add a missing absolute path to llvm-mc command.

Somehow missed this in https://codereview.chromium.org/1419173006 .

BUG= none
R=kschimpf@google.com

Review URL: https://codereview.chromium.org/1410813004 .

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