Return correct exit code from build.ps1 (#8582)

Build.cmd failed to return an actual exit code from eng/build.ps1,
which resulted in CI steps reported as "passed" despite errors
during the execution.

Author: RussKie

build.cmd

@@ -5,5 +5,5 @@ set _args=%*
 if "%~1"=="-?" set _args=-help
 if "%~1"=="/?" set _args=-help
 
-powershell -ExecutionPolicy ByPass -NoProfile -Command "& '%~dp0eng\build.ps1'" %_args%
-exit /b %ERRORLEVEL%
+powershell -ExecutionPolicy ByPass -NoProfile -Command "& '%~dp0eng\build.ps1' %_args%; exit $LASTEXITCODE"
+exit /b %ERRORLEVEL%