Add the ability to compile with profiler guided optimizations on Windows

Add the ability to compile with profiler guided optimizations on Windows

It is now possible to experiment with profiler guided optimizations when building V8. First build an instrumented sample shell:

  > scons pgo=instrument sample=shell

Then run the JavaScript code to optimize for using that sample shell. Finally build an optimized sample shell.

  > scons pgo=optimize sample=shell

Currently this does not work when building V8 as a DLL due to scons deleting v8.exp prior to the pgo=optimize step.

Due to a bug in Visual Studio (seen in version 2008) the function MessageDispatchHelperThread::Run() in debug.cc needs to be empty for this to work.
Review URL: http://codereview.chromium.org/652114

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3934 ce2b1a6d-e550-0410-aec6-3dcde31c8c00