song/StringFilter: make MatchWithoutNegation() public

src/song/StringFilter.cxx

@@ -22,7 +22,7 @@
 
 #include <assert.h>
 
-inline bool
+bool
 StringFilter::MatchWithoutNegation(const char *s) const noexcept
 {
 #if !CLANG_CHECK_VERSION(3,6)

src/song/StringFilter.hxx

@@ -105,7 +105,9 @@ public:
 	gcc_pure
 	bool Match(const char *s) const noexcept;
 
-private:
+	/**
+	 * Like Match(), but ignore the "negated" flag.
+	 */
 	gcc_pure
 	bool MatchWithoutNegation(const char *s) const noexcept;
 };