Improve backwards compatibility with GNU Make

libc/str/tprecode16to8.c

@@ -49,6 +49,9 @@ static noasan axdx_t tprecode16to8_sse2(char *dst, size_t dstsize,
 /**
  * Transcodes UTF-16 to UTF-8.
  *
+ * This is a low-level function intended for the core runtime. Use
+ * utf16toutf8() for a much better API that uses malloc().
+ *
  * @param dst is output buffer
  * @param dstsize is bytes in dst
  * @param src is NUL-terminated UTF-16 input string