codeql: Added integer overflow example

codeql/samples/integer_overflow/CMakeLists.txt

@@ -0,0 +1,5 @@
+cmake_minimum_required(VERSION 3.10)
+
+project(intof)
+
+add_executable(intof main.c)

codeql/samples/integer_overflow/main.c

@@ -0,0 +1,14 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int sum(int a, int b) { return a + b; }
+
+int main() {
+  int x = 2147483647;
+  int y = 2;
+  int z = x + sum(y, y);
+
+  printf("z = %d\n", z);
+
+  return 0;
+}