[TIMOB-12169] Create build log with compilation

Resolves https://jira.appcelerator.org/browse/TIMOB-12169
What's the point of the `logFilename` variable? It confuses. Someone could unknowingly change the definition and then replace will not work. Just write it out:

    logFile = path.join(cli.argv['project-dir'], 'build', 'build_'. + platform + '.log'),

Remove the `logFilePath` since it's not used.