Give extract-localizable-strings an option to treat warnings as errors
https://bugs.webkit.org/show_bug.cgi?id=139943

Reviewed by Darin Adler.

Add a --treat-warnings-as-errors option, which makes the script emit its warnings as errors
and exit with a non-0 return code if it emitted any warnings.

* extract-localizable-strings.pl:
Added $treatWarningsAsErrors variable, set to true if the option is passed in.

(emitWarning): Added. If $treatWarningsAsErrors is true, omits the "warning: " token from
the message, which makes it appear as an error in Xcode, and sets $sawError to 1.

Replaced all print statements that printed warnings with calls to emitWarning.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@177741 268f45cc-cd09-0410-ab3c-d52691b4dbfc