HPCC-22510 Fix OSX build break (needs #include <string>)

Signed-off-by: Jake Smith <jake.smith@lexisnexisrisk.com>

system/jlib/jsocket.cpp

@@ -24,6 +24,7 @@
     look at loopback
 */
 
+#include <string>
 #include <unordered_set>
 #include <functional>