Fixed compiler errors

* Some compilers fail to build due to the inconsistent use of the noexcept clause

Change-Id: I1f44abec84d8d0c8dd45662d1e309d006dcf9b64
Signed-off-by: Pablo Marquez Tello <pablo.tello@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/5281
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Sang-Hoon Park <sang-hoon.park@arm.com>
Reviewed-by: Manuel Bottini <manuel.bottini@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/arm_compute/core/PixelValue.h b/arm_compute/core/PixelValue.h
index f744d64..0e3d26c 100644
--- a/arm_compute/core/PixelValue.h
+++ b/arm_compute/core/PixelValue.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2020 Arm Limited.
+ * Copyright (c) 2016-2021 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -35,8 +35,11 @@
 {
 public:
     /** Default constructor: value initialized to 0 */
-    PixelValue()
-        : value{ int64_t(0) }
+    PixelValue() noexcept
+        : value
+    {
+        int64_t(0)
+    }
     {
     }
     /** Initialize the union with a pixel value of chosen datatype