*: add "noexcept" to many, many function prototypes

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

src/db/Selection.hxx

@@ -45,16 +45,16 @@ struct DatabaseSelection {
 			  const SongFilter *_filter=nullptr);
 
 	gcc_pure
-	bool IsEmpty() const;
+	bool IsEmpty() const noexcept;
 
 	/**
 	 * Does this selection contain constraints other than "base"?
 	 */
 	gcc_pure
-	bool HasOtherThanBase() const;
+	bool HasOtherThanBase() const noexcept;
 
 	gcc_pure
-	bool Match(const LightSong &song) const;
+	bool Match(const LightSong &song) const noexcept;
 };
 
 #endif