Detect AIX 4.3 or later, and if found disable the check for the thread-safe

*_r() functions as they're not needed (and if fact mess things up for us).
Brought to our attention by the friendly Troels Walsted Hansen in bug report
#696217.

configure.in

@@ -575,6 +575,22 @@ esac
 
 dnl Default is to try the thread-safe versions of a few functions
 OPT_THREAD=on
+
+dnl detect AIX 4.3 or later
+dnl see full docs on this reasoning in the lib/hostip.c source file
+AC_MSG_CHECKING([AIX 4.3 or later])
+AC_PREPROC_IFELSE([
+#if defined(_AIX) && defined(_AIX43)
+printf("just fine");
+#else
+#error "this is not AIX 4.3 or later"
+#endif
+],
+ [ AC_MSG_RESULT([yes])
+   OPT_THREAD=off ],
+ [ AC_MSG_RESULT([no]) ]
+)
+
 AC_ARG_ENABLE(thread,dnl
 [  --disable-thread       tell configure to not look for thread-safe functions],
   OPT_THREAD=off