Generation of our home-grown memmove doesn't depend on serializer state anymore.

The serializer state has to be per-Isolate, but at the point where we
generate our memmoves we don't really have an Isolate. Furthermore,
there was no fundamental reason why we shouldn't use our home-grown
memmove during mksnapshot time.

Perhaps we can totally remove our own memmove nowadays, but this would
be a separate CL.

BUG=359977
LOG=y
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/261903002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21116 ce2b1a6d-e550-0410-aec6-3dcde31c8c00