Further narrow the use of the icc 9.1 optimizer workaround.

Previous workaround proved useful, and finally did not trigger any warning!

lib/curl_addrinfo.c

@@ -69,7 +69,7 @@
  */
 
 #if defined(__INTEL_COMPILER) && (__INTEL_COMPILER == 910) && \
-    defined(__unix__) &&  defined(__i386__)
+    defined(__OPTIMIZE__) && defined(__unix__) &&  defined(__i386__)
   /* workaround icc 9.1 optimizer issue */
 # define vqualifier volatile
 #else