configure: fix detection of re-entrant resolver functions

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