LLVM IR is relatively agnostic, but not so much so that you can use it to recompile for another architecture (unless you take effort to design an entire ABI to work around the platform-specific things that creep into it, as Apple did with arm64_32).
IIRC, LLVM IR has ABI, word length, and endianness baked in so you could generate IR that's portable to, say, any 32-bit LE processor. Basically that was Chrome PNaCl.
It's interesting how not having the source code drove technology in the 90's.