Fix ARM64 build after r23744.

TBR=yangguo@chromium.org

Review URL: https://codereview.chromium.org/547683002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23746 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Disable broken JSLoadContext typer.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/542193002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23747 ce2b1a6d-e550-0410-aec6-3dcde31c8c00