[clang] [llvm] [RISCV] Add back SiFive's cdiscard.d.l1 and cflush.d.l1 instructions. (PR #83896)

[Yingwei Zheng via cfe-commits]

================
@@ -60,6 +60,8 @@
 // CHECK-NOT: __riscv_xsfvfwmaccqqq {{.*$}}
 // CHECK-NOT: __riscv_xsfqmaccdod {{.*$}}
 // CHECK-NOT: __riscv_xsfvqmaccqoq {{.*$}}
+// CHECK-NOT: __riscv_sifivecdiscarddlone {{.*$}}
+// CHECK-NOT: __riscv_sifivecflushdlone {{.*$}}
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dtcxzyw wrote:

```suggestion
// CHECK-NOT: __riscv_xsifivecdiscarddlone {{.*$}}
// CHECK-NOT: __riscv_xsifivecflushdlone {{.*$}}
```

https://github.com/llvm/llvm-project/pull/83896