Sorry but you can't compile Alchemy stuff like AS3.h in visual studio hoping to debug your application
You may develop your C/C++ code in visual studio as a "portable application" to alchemy or whatever platform you like, so you may develop , debug it, and then recompile the whole application in alchemy ... you will need a lot of #ifdef/#endif and so on to make it.
If you have isolated pieces of C/C++ code build up a test application and test it.. maybe it's easier.
if you really need to debug the alchemy version of your code you could follow this post, it's a great starting point.
i hope it could help