arch: Adding missing override to PCState.set

As highlighed in this failing compiler test:
https://github.com/gem5/gem5/actions/runs/6348223508/job/17389057995

Clang was failing when compiling "build/ALL/gem5.opt" due missing
overrides in `PCState`'s "set" function.

This was observed in Clang-14 and, stangely, Clang-8.

Change-Id: I240c1087e8875fd07630e467e7452c62a5d14d5b

src/arch/arm/pcstate.hh

@@ -92,7 +92,7 @@ class PCState : public GenericISA::UPCState<4>
 
   public:
     void
-    set(Addr val)
+    set(Addr val) override
     {
         Base::set(val);
         npc(val + (thumb() ? 2 : 4));

src/arch/generic/pcstate.hh

@@ -489,7 +489,7 @@ class DelaySlotPCState : public SimplePCState<InstWidth>
     void nnpc(Addr val) { _nnpc = val; }
 
     void
-    set(Addr val)
+    set(Addr val) override
     {
         Base::set(val);
         nnpc(val + 2 * InstWidth);
@@ -563,7 +563,7 @@ class DelaySlotUPCState : public DelaySlotPCState<InstWidth>
     }
 
     void
-    set(Addr val)
+    set(Addr val) override
     {
         Base::set(val);
         this->upc(0);

src/arch/x86/pcstate.hh

@@ -66,7 +66,7 @@ class PCState : public GenericISA::UPCState<8>
     }
 
     void
-    set(Addr val)
+    set(Addr val) override
     {
         Base::set(val);
         _size = 0;