Bug 909826 - Change x86/x64 GenerateEntry to be more like ARM (r=bbouvier)

--HG--
extra : rebase_source : 04e5454e6bb4526875246bc1ca374764d5a8eb39
Bug 909826 - Merge x86/x64 and ARM GenerateEntry paths (r=mjrosenb)

--HG--
extra : rebase_source : 13b85d280ba675860cd48aa8542526b3da56c274
Bug 909826 - Tidy up stack overflow exit (r=mjrosenb)

--HG--
extra : rebase_source : d1df34f829ec031e027cad7b05146b6987251c26