Support building with or without unaligned accesses by using scons flag simulatorunalignedaccesses.

$ scons simulator=arm simulatorunalignedaccesses=off
$ scons simulator=arm simulatorunalignedaccesses=on

If simulatorunalignedaccesses is not specified (or specified as default) the default is to use unaligned accesses.
Review URL: http://codereview.chromium.org/2218003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4737 ce2b1a6d-e550-0410-aec6-3dcde31c8c00