Subzero. Misc fixes.

This CL disables the X86 assembler tests by default. They take too long
to compile, so there's very little point in running them with the other
unittests.

This CL fixes a bug introduced in
https://codereview.chromium.org/1260163003/ that caused liveness
analysis to assert due to a uninitialized Variable.

BUG=
R=jvoung@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/1266863002.
2 files changed