x86 support

[christoph-hart]

So I tried to compile NativeJIT with the x86 architecture (using VS2015 on Win7) and stumbled over the following roadblocks:

1. Missing BitOperations (popcnt64, etc) - easily replacable by two calls to their 32bit counterpart
2. Missing RUNTIME_FUNCTION macro (+ some other stuff for stack unwinding) - fixed by using the dummy struct from Unix (I can live with missing stack unwinding on x86, since it doesn't work on Unix systems, I hardly use it anyway)
3. #error because of missing _AMD64_ flag - just commented out :)

Now these three were easy, but now it gets a little bit more complicated:

3. A ton of compilation errors in the Emit functions because the compiler can't implicitely convert NativeJIT::BaseRegister to NativeJIT::Register<8U, false>. Adding a explicit C-style cast "fixes" those, but I am pretty sure this is not a solution.
4. Hitting the static_assert in the ExpressionTree::Temporary() method: "The size of the variable is too large."
5. Some compilation errors when trying to static_cast<> a value to an unsigned int (something like that). This is where I stopped trying :)

This is way too far in the guts of NativeJIT's internals for me to be able to say if trying to support x86 makes any sense at all.

[stonedreamforest]

any plan?