[llvm] [Exegesis][RISCV] Add RISCV support for llvm-exegesis (PR #89047)

[via llvm-commits]

================
@@ -291,6 +297,22 @@ T ExitOnFileError(const Twine &FileName, Expected<T> &&E) {
   return std::move(*E);
 }
 
+static const char *getIgnoredOpcodeReasonOrNull(const LLVMState &State,
----------------
AnastasiyaChernikova wrote:

Removed this check from tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp, since the program always first goes to generateSnippets in the file tools/llvm-exegesis/llvm-exegesis.cpp, where the same check already done and returns an error if it fails

https://github.com/llvm/llvm-project/pull/89047