Add a function that's missing from musl, use autotools machinery to
use it when needed
https://bugs.gentoo.org/880341
--- a/configure.in
+++ b/configure.in
@@ -191,6 +191,8 @@
 	[Define to unsigned int if you dont have it])]
 )
 
+AC_REPLACE_FUNCS([inet_nsap_ntoa])
+
 AC_MSG_CHECKING([whether our compiler supports __func__])
 AC_TRY_COMPILE([],
  [void foo() { const char *cp = __func__; }],
--- a/inet_nsap_ntoa.c
+++ b/inet_nsap_ntoa.c
@@ -0,0 +1,50 @@
+/* taken from glibc source */
+/*
+ * Copyright (c) 1996-1999 by Internet Software Consortium.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
+ * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
+ * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+ * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+ * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
+ * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+ * SOFTWARE.
+ */
+
+#if !defined(HAVE_INET_NSAP_NTOA)
+#include <sys/types.h>
+
+char *
+inet_nsap_ntoa(int binlen, const u_char *binary, char *ascii) {
+	int nib;
+	int i;
+	static char tmpbuf[255*2 + 128];
+	char *start;
+
+	if (ascii)
+		start = ascii;
+	else {
+		ascii = tmpbuf;
+		start = tmpbuf;
+	}
+
+	if (binlen > 255)
+		binlen = 255;
+
+	for (i = 0; i < binlen; i++) {
+		nib = *binary >> 4;
+		*ascii++ = nib + (nib < 10 ? '0' : '7');
+		nib = *binary++ & 0x0f;
+		*ascii++ = nib + (nib < 10 ? '0' : '7');
+		if (((i % 2) == 0 && (i + 1) < binlen))
+			*ascii++ = '.';
+	}
+	*ascii = '\0';
+	return (start);
+}
+#endif
--- a/res_debug.c
+++ b/res_debug.c
@@ -94,6 +94,10 @@
 #include "dnsres-internal.h"
 #include "resolv.h"
 
+#if !defined(HAVE_INET_NSAP_NTOA)
+char *inet_nsap_ntoa(int binlen, const u_char *binary, char *ascii);
+#endif
+
 /* Signatures */
                                         /* Size of a mod or exp in bits */
 #define MIN_MD5RSA_KEY_PART_BITS         512