arch-riscv,misc: Fix clang missing override errors

Clang 9 failed to compile RISC-V due to missing overrides in
`src/arch/riscv/remote_gdb.hh`. This commit adds these missing
overrides.

Change-Id: Id0bfc371ca3e3e1b91e9112a837e1862072bf9d2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40395
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/riscv/remote_gdb.hh

@@ -147,14 +147,15 @@ class RemoteGDB : public BaseRemoteGDB
      * GDB then queries for xml blobs using qXfer:features:read:xxx.xml
      */
     std::vector<std::string>
-    availableFeatures() const
+    availableFeatures() const override
     {
         return {"qXfer:features:read+"};
     };
     /**
      * Reply to qXfer:features:read:xxx.xml qeuries
      */
-    bool getXferFeaturesRead(const std::string &annex, std::string &output);
+    bool getXferFeaturesRead(const std::string &annex,
+                             std::string &output) override;
 };
 
 } // namespace RiscvISA