The FP setting is different for X32 than the other platforms as
kFPOnStackSize is double the kPointerSize and we have to clear the
higher 32 bits to 0.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/20073004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15966 ce2b1a6d-e550-0410-aec6-3dcde31c8c00