Disable maybe-uninitialized warning in GCC 4.8
https://bugs.webkit.org/show_bug.cgi?id=119835

Reviewed by Anders Carlsson.

Disable the maybe-uninitialized warning.

* wtf/Compiler.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154381 268f45cc-cd09-0410-ab3c-d52691b4dbfc