[llvm] [ORC-RT] Initial check-in for a new, top-level ORC runtime project. (PR #113499)

[Chris B via llvm-commits]

llvm-beanz wrote:

The compiler-rt Darwin build is a sin of mine that should not be repeated. Unfortunately it isn't something someone outside Apple can really fix because Apple has a hard dependency on it for Clang builds. The only reason why the compiler-rt build generates fat archives was because I was required by management to ensure that the Apple Clang builds with CMake produced _identical_ outputs to the autoconf builds (a ridiculous request that I'm still bitter about almost a decade later).

I always felt that it was probably better to have darwin build thin-libraries and even put them in separate directories structured the way the Linux toolchain does. That would allow simplifying a lot of logic in the darwin driver too. Since the driver always generates single-architecture compile and link commands and uses lipo to merge objects when building fat binaries, there is no reason that fat archives are strictly needed. 

https://github.com/llvm/llvm-project/pull/113499