[Orc] Initial version of ELFSymtabStaticGenerator

[stmonty]

Hello! This is my first contribution attempt here. I have been working with on jank which uses the Orcv2 machinery for the JIT compilation. I think @lhames might know about this.

One problem we have encountered was that when the Jank binary was fully statically built no symbols were able to be found. This PR ties to remedy that for ELF binaries by opening the current binary and using the symtab portion of the ELF binary to find missing symbols.

Any comments for improvements are greatly appreciated!

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