[llvm] [llvm-c] Improve TargetMachine bindings (PR #70806)

[Duncan P. N. Exon Smith via llvm-commits]

dexonsmith wrote:

(Removed myself from the review list, since I wouldn't say I'm up enough on either TargetMachine or the C API.)

https://github.com/llvm/llvm-project/pull/70806