[EFL] build-webkit should try harder to avoid re-running cmake
https://bugs.webkit.org/show_bug.cgi?id=137949

Reviewed by Martin Robinson.

* Scripts/webkitdirs.pm:
(shouldRemoveCMakeCache): Don't remove CMakeCache unconditionally for EFL.
(generateBuildSystemFromCMakeProject): Comment fix after r174681.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@175327 268f45cc-cd09-0410-ab3c-d52691b4dbfc