Unreviewed, rolling out r168451.
https://bugs.webkit.org/show_bug.cgi?id=132670

Not a speed-up, just do what other compilers do. (Requested by
kling on #webkit).

Reverted changeset:

"[X86] Emit BT instruction for single-bit tests."
https://bugs.webkit.org/show_bug.cgi?id=132650
http://trac.webkit.org/changeset/168451

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@168461 268f45cc-cd09-0410-ab3c-d52691b4dbfc