SymbolDB: Default constructor and destructor within the cpp file

Given this is a class with non-trivial data-members, it's preferable to
default the constructor and destructor in the cpp file.

Source/Core/Common/SymbolDB.cpp

@@ -20,6 +20,10 @@ static std::string GetStrippedFunctionName(const std::string& symbol_name)
   return name;
 }
 
+SymbolDB::SymbolDB() = default;
+
+SymbolDB::~SymbolDB() = default;
+
 void Symbol::Rename(const std::string& symbol_name)
 {
   this->name = symbol_name;

Source/Core/Common/SymbolDB.h

@@ -62,8 +62,9 @@ public:
   using XFuncMap = std::map<u32, Symbol>;
   using XFuncPtrMap = std::map<u32, std::set<Symbol*>>;
 
-  SymbolDB() {}
-  virtual ~SymbolDB() {}
+  SymbolDB();
+  virtual ~SymbolDB();
+
   virtual Symbol* GetSymbolFromAddr(u32 addr) { return nullptr; }
   virtual Symbol* AddFunction(u32 start_addr) { return nullptr; }
   void AddCompleteSymbol(const Symbol& symbol);