Only disabling LLVMSymbolSearching on Windows platforms

I'm struggling to get axe to build correctly on Windows >.< but once I have, I'll see if I can reproduce the bug there. Assuming it's not present then this patch should be all that's needed. If it is, however, I'll try and follow up with something better. 

At a guess, and from what you've suggested, it'll probably mean changes to the `genGlobalJitMap` utility -- though I still have no great ideas on how to find all the symbols which might be needed, unless I add  everything from the GCC runtime (though this seems like a *bad* idea).

## Commit message
An error occurs on 32 bit linux, where it isn't finding all the
symbols needed at run time, and failing.

I've not checked behaviour on Windows x86 yet. Windows x86_64
should remain unaffected.