[check-iwyu] Do not fail right away if IWYU_TOOL fails
Since only newer versions of IWYU_TOOL fail with an exit code, we have to disable -e around the IWYU_TOOL invocation. Otherwise we would not print IWYU_LOG.
Since only newer versions of IWYU_TOOL fail with an exit code, we have to disable -e around the IWYU_TOOL invocation. Otherwise we would not print IWYU_LOG.