util/StringAPI: add memrchr() wrapper

src/util/StringAPI.hxx

@@ -94,6 +94,27 @@ StringFindLast(char *haystack, char needle) noexcept
 	return strrchr(haystack, needle);
 }
 
+gcc_pure gcc_nonnull_all
+static inline const char *
+StringFindLast(const char *haystack, char needle, size_t size) noexcept
+{
+#if defined(__GLIBC__) || defined(__BIONIC__)
+	/* memrchr() is a GNU extension (and also available on
+	   Android) */
+	return (const char *)memrchr(haystack, needle, size);
+#else
+	/* emulate for everybody else */
+	const auto *p = haystack + size;
+	while (p > haystack) {
+		--p;
+		if (*p == needle)
+			return p;
+	}
+
+	return nullptr;
+#endif
+}
+
 gcc_pure gcc_nonnull_all
 static inline const char *
 StringFindAny(const char *haystack, const char *accept) noexcept