COMPMID-765: Added missing <errno.h> include

Change-Id: I25424481ddbbeb43f940cf51cef791e4fd83ea92
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/117676
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Reviewed-by: Pablo Tello <pablo.tello@arm.com>
Tested-by: Jenkins <bsgcomp@arm.com>
diff --git a/tests/framework/instruments/PMU.h b/tests/framework/instruments/PMU.h
index e0a1870..c069a63 100644
--- a/tests/framework/instruments/PMU.h
+++ b/tests/framework/instruments/PMU.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017 ARM Limited.
+ * Copyright (c) 2017-2018 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -27,6 +27,7 @@
 #include "arm_compute/core/Error.h"
 
 #include <cstdint>
+#include <errno.h>
 #include <linux/perf_event.h>
 #include <stdexcept>
 #include <sys/syscall.h>