[mlir] [llvm] fix linking on riscv64 (PR #74167)

[Vincent Palatin via llvm-commits]

vpalatin wrote:

@abrachet 
The line I'm uncommenting was originally commented out by your change https://reviews.llvm.org/D137799
maybe you have something to say about the rationale

https://github.com/llvm/llvm-project/pull/74167