no-memfd in-memory elf execution (extends #79)

[darrenmartyn]

As an extension of #79, I came across this, which actually does the whole goddamn thing I'd been trying to get at, and documents it pretty well:

https://github.com/arget13/DDexec

I'll try add it to Orc at some point in the future as a way to get file-less memexec of ELF files on kernels before memfd support was added.