Previous fix (COIN-1133) by adding $? works only to show last operation status True/False.

But in provisioning scripts are running inside a wrapper and if something fails (like ffmpeg again)

• Script is sending Exit Code 1 (with Exit 1)
• This cannot be read in Coin via $?

Fortunately Windows has $LastExitCode which works better in cases like this to show the last exit code 0 or 1 (or other integer).

Fix:

• Change $? with $LastExitCode

Background

• Issue happened with Win 10 provisioning was passing although ffmpeg installation had failed
• Issue visible in this review: https://codereview.qt-project.org/c/qt/qt5/+/662914
• Testresults example: https://testresults.qt.io/coin/integration/qt/qt5/tasks/1753733036 
• Win 10 provisioning which was available from cache: https://testresults.qt.io/coin/api/log/provisioning/qtci-windows-10_22H2-x86_64-53-1202f7/provision_1753493360/log.txt.gz 
• Installing ffmpeg has verification which will exit with exit code 1, but $? didn't catch that

Example in log:

ERROR: zlib requested but not found
If you think configure made a mistake, make sure you are using the latest
version from Git.  If the latest version fails, report the problem to the
ffmpeg-user@ffmpeg.org mailing list or IRC #ffmpeg on irc.libera.chat.
Include the log file "ffbuild/config.log" produced by configure as this will help
solve the problem.
Failed to build FFmpeg for msvc-arm64
Ffmpeg installation results:
  mingw: OK
  llvm-mingw: OK
  android-armv7: OK
  msvc: FAIL
  msvc-arm64: FAIL