Unreviewed, rolling out r198235, r198240, r198241, and

Unreviewed, rolling out r198235, r198240, r198241, and
r198252.

Causing crashes on ARM

Reverted changesets:

"Remove compile time define for SEPARATED_HEAP"
https://bugs.webkit.org/show_bug.cgi?id=155508
http://trac.webkit.org/changeset/198235

"Gardening: build fix after r198235."
http://trac.webkit.org/changeset/198240

"Build fix."
http://trac.webkit.org/changeset/198241

"Rename performJITMemcpy to something more inline with our
normal webkit function names"
https://bugs.webkit.org/show_bug.cgi?id=155525
http://trac.webkit.org/changeset/198252

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@198291 268f45cc-cd09-0410-ab3c-d52691b4dbfc