[llvm] [RISCV] improve `musttail` support (PR #170547)

[Folkert de Vries via llvm-commits]

================
@@ -23678,29 +23643,28 @@ bool RISCVTargetLowering::isEligibleForTailCallOptimization(
   if (Caller.hasFnAttribute("interrupt"))
----------------
folkertdev wrote:

based on the updated tests it seems fine in terms of efficiency. 

https://github.com/llvm/llvm-project/pull/170547