Add support for compiling for ESX

With contributions from Ryan Haynes <rhaynes@fusionio.com>

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/backend.c b/backend.c
index 23fa345..ee75566 100644
--- a/backend.c
+++ b/backend.c
@@ -1575,7 +1575,7 @@
 	struct thread_data *td;
 	void *data, *ret;
 
-#ifndef __hpux
+#if !defined(__hpux) && !defined(CONFIG_NO_SHM)
 	data = shmat(shmid, NULL, 0);
 	if (data == (void *) -1) {
 		int __err = errno;