Improve test coverage for %zx, %zu used with printf

test/testio.cpp

@@ -1796,6 +1796,12 @@ private:
               "}");
         ASSERT_EQUALS("", errout.str());
 
+        check("void foo(int i, long double ld) {\n"
+              "  printf(\"%zx %zu\", i, ld);\n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:2]: (warning) %zx in format string (no. 1) requires 'size_t' but the argument type is 'signed int'.\n"
+                      "[test.cpp:2]: (warning) %zu in format string (no. 2) requires 'size_t' but the argument type is 'long double'.\n", errout.str());
+
         // False negative test
         check("void foo(unsigned int i) {\n"
               "  printf(\"%h\", i);\n"