[RISCV] Fix incorrect elf attributes name

[Jim]

Summary

According to https://github.com/riscv/riscv-elf-psabi-doc/pull/71, the elf attributes name should have Tag_RISCV prefix.

llvm/lib/Support/RISCVAttributes.cpp

 //===-- RISCVAttributes.cpp - RISCV Attributes ----------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/RISCVAttributes.h"
 
 using namespace llvm;
 using namespace llvm::RISCVAttrs;
 
 static const TagNameItem tagData[] = {
-    {STACK_ALIGN, "Tag_stack_align"},
-    {ARCH, "Tag_arch"},
-    {UNALIGNED_ACCESS, "Tag_unaligned_access"},
-    {PRIV_SPEC, "Tag_priv_spec"},
-    {PRIV_SPEC_MINOR, "Tag_priv_spec_minor"},
-    {PRIV_SPEC_REVISION, "Tag_priv_spec_revision"},
+    {STACK_ALIGN, "Tag_RISCV_stack_align"},
+    {ARCH, "Tag_RISCV_arch"},
+    {UNALIGNED_ACCESS, "Tag_RISCV_unaligned_access"},
+    {PRIV_SPEC, "Tag_RISCV_priv_spec"},
+    {PRIV_SPEC_MINOR, "Tag_RISCV_priv_spec_minor"},
+    {PRIV_SPEC_REVISION, "Tag_RISCV_priv_spec_revision"},
 };
 
 const TagNameMap llvm::RISCVAttrs::RISCVAttributeTags(tagData,
                                                       sizeof(tagData) /
                                                           sizeof(TagNameItem));