Backtrace() and backtrace_symbols() API are not supported on
AIX and there are no user-mode equivalent API for the same.
For now, disabling the call to those API.
Currently this is preventing V8 to build on AIX.
This debug functionality was added in
https://codereview.chromium.org/2248393002

R=rmcilroy@chromium.org

BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2324453002
Cr-Commit-Position: refs/heads/master@{#39356}