Codechange: Use override specifer for overriding member declarations

This is a C++11 feature that allows the compiler to check that a virtual
member declaration overrides a base-class member with the same signature.

Also src/blitter/32bpp_anim_sse4.hpp +38 is no longer erroneously marked
as virtual despite being a template.

src/strgen/strgen.cpp

@@ -115,14 +115,14 @@ struct FileStringReader : StringReader {
 		fclose(this->fh);
 	}
 
-	/* virtual */ char *ReadLine(char *buffer, const char *last)
+	char *ReadLine(char *buffer, const char *last) override
 	{
 		return fgets(buffer, ClampToU16(last - buffer + 1), this->fh);
 	}
 
-	/* virtual */ void HandlePragma(char *str);
+	void HandlePragma(char *str) override;
 
-	/* virtual */ void ParseFile()
+	void ParseFile() override
 	{
 		this->StringReader::ParseFile();