configure: fix detection of re-entrant resolver functions

uClibc does not provide res_nsearch:
asterisk-16.0.0/main/dns.c:506: undefined reference to `res_nsearch'

Patch coded by Yann E. MORIN:
http://lists.busybox.net/pipermail/buildroot/2018-October/232630.html

ASTERISK-21795 #close

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
[Retrieved from:
https: //git.buildroot.net/buildroot/tree/package/asterisk/0005-configure-fix-detection-of-re-entrant-resolver-funct.patch]
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Change-Id: I79296f19e28ec764bbd1e991bf11c416d0b10563
(cherry picked from commit a10b4f5d2c)

configure

@@ -19663,7 +19663,11 @@ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 int
 main ()
 {
-int foo = res_ninit(NULL);
+
+				int foo;
+				foo = res_ninit(NULL);
+				foo = res_nsearch(NULL, NULL, 0, 0, NULL, 0);
+
   ;
   return 0;
 }

configure.ac

@@ -1494,7 +1494,11 @@ AC_LINK_IFELSE(
 			#include <arpa/nameser.h>
 			#endif
 			#include <resolv.h>],
-			[int foo = res_ninit(NULL);])],
+			[
+				int foo;
+				foo = res_ninit(NULL);
+				foo = res_nsearch(NULL, NULL, 0, 0, NULL, 0);
+			])],
 	AC_MSG_RESULT(yes)
 	AC_DEFINE([HAVE_RES_NINIT], 1, [Define to 1 if your system has the re-entrant resolver functions.])
 	AC_SEARCH_LIBS(res_9_ndestroy, resolv)