[RISCV] Add -print-pipeline-passes test as follow up to #156798. NFC (#157011)

Author: topperc

llvm/test/CodeGen/RISCV/print-pipeline-passes.ll

@@ -0,0 +1,12 @@
+; RUN: opt -mtriple=riscv32 -S -passes='default<O0>' -print-pipeline-passes < %s | FileCheck --check-prefix=O0 %s
+; RUN: opt -mtriple=riscv64 -S -passes='default<O0>' -print-pipeline-passes < %s | FileCheck --check-prefix=O0 %s
+; RUN: opt -mtriple=riscv32 -S -passes='default<O2>' -print-pipeline-passes < %s | FileCheck %s
+; RUN: opt -mtriple=riscv64 -S -passes='default<O2>' -print-pipeline-passes < %s | FileCheck %s
+
+; CHECK: loop-idiom-vectorize
+; O0-NOT: loop-idiom-vectorize
+
+define void @foo() {
+entry:
+  ret void
+}