Add check for netdb.h and getaddrinfo to configure.ac

Extracted from octo/libmodbus ff/ipv6 a6ae017c82e

configure.ac

@@ -78,6 +78,7 @@ AC_CHECK_HEADERS([ \
     netinet/in.h \
     netinet/tcp.h \
     arpa/inet.h \
+    netdb.h \
 ])
 
 # Checks for header files.
@@ -98,7 +99,7 @@ AC_CHECK_DECLS([__CYGWIN__])
 
 # Checks for library functions.
 AC_FUNC_FORK
-AC_CHECK_FUNCS([gettimeofday inet_ntoa memset select socket strerror strlcpy])
+AC_CHECK_FUNCS([gettimeofday inet_ntoa memset select socket strerror strlcpy getaddrinfo])
 
 # Add -Wall -Werror for GCC if not already there
 if test "x$GCC" = "xyes"; then