Add cases in dead code test where the arrays are constexpr.

Complemeting previous case where the integers used for the sizes of the
arrays were constexpr.

Author: fjatWbyT

cpp/common/test/rules/deadcode/DeadCode.expected

@@ -14,3 +14,4 @@
 | test.cpp:79:17:80:3 | { ... } | This statement is dead code. |
 | test.cpp:85:3:85:44 | declaration | This statement is dead code. |
 | test.cpp:87:3:87:30 | declaration | This statement is dead code. |
+| test.cpp:90:3:90:50 | declaration | This statement is dead code. |

cpp/common/test/rules/deadcode/test.cpp

@@ -86,5 +86,8 @@ int test_dead_code(int x) {
 
   constexpr int unused_int{2}; // NON_COMPLIANT
 
-  return live5 + live6; // COMPLIANT
-}
+  constexpr int   constexpr_used_array[]{3, 4, 5}; // COMPLIANT
+  constexpr int constexpr_unused_array[]{0, 1, 2}; // NON_COMPLIANT
+
+  return live5 + live6 + constexpr_used_array[1]; // COMPLIANT
+}