COMPMID-2486: Remove/add disabled compiler warnings

Removed the following flags:
-Wno-vla
-Wno-strict-overflow

Added:
-Wformat-security

Change-Id: I49eb3d724e14db796e543164295674617c37cb65
Signed-off-by: Michalis Spyrou <michalis.spyrou@arm.com>
Reviewed-on: https://review.mlplatform.org/c/2109
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michele Di Giorgio <michele.digiorgio@arm.com>
diff --git a/tests/framework/instruments/MaliCounter.h b/tests/framework/instruments/MaliCounter.h
index a3cc446..94ef93f 100644
--- a/tests/framework/instruments/MaliCounter.h
+++ b/tests/framework/instruments/MaliCounter.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2018 ARM Limited.
+ * Copyright (c) 2017-2019 ARM Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -86,7 +86,7 @@
     const char *const  _device
     { "/dev/mali0"
     };
-    int                _num_cores{ 0 };
+    uint32_t           _num_cores{ 0 };
     uint32_t           _hw_ver{ 0 };
     int                _buffer_count{ 16 };
     size_t             _buffer_size{ 0 };