Also make configure check non-fatal

Author: arnaud-lb

ext/opcache/config.m4

@@ -345,9 +345,9 @@ PHP_ADD_EXTENSION_DEP(opcache, date)
 PHP_ADD_EXTENSION_DEP(opcache, pcre)
 
 if test "$php_cv_shm_ipc" != "yes" && test "$php_cv_shm_mmap_posix" != "yes" && test "$php_cv_shm_mmap_anon" != "yes"; then
-  AC_MSG_FAILURE(m4_text_wrap([
+  AC_MSG_WARN(m4_text_wrap([
     No supported shared memory caching support was found when configuring
-    opcache.
+    opcache. Opcache will be disabled.
   ]))
 fi