cmake: Fix ntohll and htonll macro detection.

BUG: https://red.libssh.org/issues/164

Thanks to Ryan Schmidt!

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>

ConfigureChecks.cmake

@@ -104,8 +104,8 @@ check_function_exists(snprintf HAVE_SNPRINTF)
 check_function_exists(poll HAVE_POLL)
 check_function_exists(select HAVE_SELECT)
 check_function_exists(getaddrinfo HAVE_GETADDRINFO)
-check_function_exists(ntohll HAVE_NTOHLL)
-check_function_exists(htonll HAVE_HTONLL)
+check_symbol_exists(ntohll arpa/inet.h HAVE_NTOHLL)
+check_symbol_exists(htonll arpa/inet.h HAVE_HTONLL)
 
 if (WIN32)
     check_function_exists(_strtoui64 HAVE__STRTOUI64)