contrib: c++ify test stubs after switching to c++ compilers

contrib/devtools/test-security-check.py

@@ -15,10 +15,10 @@ from utils import determine_wellknown_cmd
 def write_testcode(filename):
     with open(filename, 'w', encoding="utf8") as f:
         f.write('''
-    #include <stdio.h>
+    #include <cstdio>
     int main()
     {
-        printf("the quick brown fox jumps over the lazy god\\n");
+        std::printf("the quick brown fox jumps over the lazy god\\n");
         return 0;
     }
     ''')

contrib/devtools/test-symbol-check.py

@@ -57,11 +57,11 @@ class TestSymbolChecks(unittest.TestCase):
         executable = 'test3'
         with open(source, 'w', encoding="utf8") as f:
             f.write('''
-                #include <stdio.h>
+                #include <cstdio>
 
                 int main()
                 {
-                    printf("42");
+                    std::printf("42");
                     return 0;
                 }
         ''')