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/validation/reference/YOLOLayer.cpp b/tests/validation/reference/YOLOLayer.cpp
index cf5e256..0011b85 100644
--- a/tests/validation/reference/YOLOLayer.cpp
+++ b/tests/validation/reference/YOLOLayer.cpp
@@ -46,7 +46,8 @@
     const T a(info.a());
     const T b(info.b());
 
-    for(int i = 0; i < src.num_elements(); ++i)
+    const uint32_t num_elements = src.num_elements();
+    for(uint32_t i = 0; i < num_elements; ++i)
     {
         const size_t z = index2coord(dst.shape(), i).z() % (num_classes + 5);