add context save for GenerateFastApiCall

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/23461039

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16744 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Refactoring only: Make it clear that MOD is special.

LArithmeticD should really be 5 different instructions... :-/

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/23800005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16745 ce2b1a6d-e550-0410-aec6-3dcde31c8c00