Explicitly test for malloc_trim() in configure

src/internfile/mh_xslt.cpp

@@ -52,9 +52,9 @@ public:
 			// malloc_trim() and mallopt() doc seems to be a bit
 			// misleading, there is probably a frag size under which
 			// free() does not try to malloc_trim() at all
-#ifndef _WIN32
+#ifdef HAVE_MALLOC_TRIM
 			malloc_trim(0);
-#endif
+#endif /* HAVE_MALLOC_TRIM */
         }
     }