Fix the remaining few warnings that Clang catches

customext/cflush.cc

@@ -19,7 +19,7 @@ static reg_t custom_cflush(processor_t* p, insn_t insn, reg_t pc)
 class cflush_t : public extension_t
 {
  public:
-  const char* name() const { return "cflush"; }
+  const char* name() const override { return "cflush"; }
 
   cflush_t() {}
 

fesvr/htif.cc

@@ -158,11 +158,9 @@ void htif_t::load_symbols(std::map<std::string, uint64_t>& symbols)
 {
   class nop_memif_t : public memif_t {
    public:
-    nop_memif_t(htif_t* htif) : memif_t(htif), htif(htif) {}
+    nop_memif_t(htif_t* htif) : memif_t(htif) {}
     void read(addr_t UNUSED addr, size_t UNUSED len, void UNUSED *bytes) override {}
     void write(addr_t UNUSED taddr, size_t UNUSED len, const void UNUSED *src) override {}
-   private:
-    htif_t* htif;
   } nop_memif(this);
 
   reg_t nop_entry;

spike_main/spike-log-parser.cc

@@ -38,7 +38,6 @@ int main(int UNUSED argc, char** argv)
 
   std::regex reg("^core\\s+\\d+:\\s+0x[0-9a-f]+\\s+\\(0x([0-9a-f]+)\\)", std::regex_constants::icase);
   std::smatch m;
-  std::ssub_match sm ;
 
   while (getline(cin,s)){
     if (regex_search(s, m, reg)){