Add possibility of passing parameters to build-webkit by environment variable,
because the buildbot slaves can't control the arguments.

Patch by Gabor Rapcsanyi <rgabor@inf.u-szeged.hu> on 2010-02-09
Reviewed by Tor Arne Vestbø.

* Scripts/build-webkit:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@54548 268f45cc-cd09-0410-ab3c-d52691b4dbfc