fix run_clang_tidy.sh error printing

[rockwotj]

The trap wasn't firing before, so rewrite as an if statement.

Fixes: #92

[erenon]

hi, thanks for the submission. do you know why wasn't the trap firing?

[rockwotj]

I'm not fully sure, check out this simple reproducer:

#!/usr/bin/env bash
set -ue
# Print output on failure only
logfile="$(mktemp)"
trap 'if (($?)); then cat "$logfile" 1>&2; fi; rm "$logfile"' EXIT

{
  echo "WHAT IS GOING ON HERE" && false
} >"$logfile" 2>&1

Interestingly if I remove set -ue the script works as intended.

[rockwotj]

Specifically it's the set -e that is causing issues.

In Bash, set -e (also written as set -o errexit) makes the script exit immediately if any command returns a non-zero exit status—which typically indicates an error.

I don't have enough bash fu to know why that causes the issues...

[rockwotj]

Ping @erenon

[rockwotj]

Ping @erenon

[dotnwat]

this fixes the problem for me

[rockwotj]

Last ping @erenon, thanks!

[erenon]

Thanks! merging.