[clang-tidy] use nodiscard

Introduced in C++17. It replaces gcc's warn_unused_result.

Found with modernize-use-nodiscard.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/input/plugins/FileInputPlugin.cxx

@@ -43,7 +43,7 @@ public:
 
 	/* virtual methods from InputStream */
 
-	bool IsEOF() const noexcept override {
+	[[nodiscard]] bool IsEOF() const noexcept override {
 		return GetOffset() >= GetSize();
 	}