oe-selftest: add a cpp-example recipe

This simple C++ project supports compilation with CMake and Meson.
(Autotool support could be added later on.)
It's supposed to be used with oe-selftest.

An artificial project has several advantages over compiling a normal
CMake or Meson based project for testing purposes:
- It is much faster because it can be kept minimalistic
- It can cover multiple odd corner cases
- No one will change it in an unpredictable way
- It can support multiple build tools with only one C++ codebase

(From OE-Core rev: 4904e772470b0d6e5d98ef0344b3f2bf54214661)

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-selftest/recipes-test/cpp/files/test-cpp-example.cpp

@@ -0,0 +1,25 @@
+/*
+* Copyright OpenEmbedded Contributors
+*
+* SPDX-License-Identifier: MIT
+*/
+
+#include "cpp-example-lib.hpp"
+
+#include <iostream>
+
+/* This is for creating a failing test for testing the test infrastructure */
+#ifndef FAIL_COMPARISON_STR
+#define FAIL_COMPARISON_STR ""
+#endif
+
+int main() {
+    auto cpp_example = CppExample();
+    auto ret_string = cpp_example.get_string();
+    if(0 == ret_string.compare(CppExample::test_string + FAIL_COMPARISON_STR)) {
+        std::cout << "PASS: " << ret_string << " = " << CppExample::test_string << std::endl;
+    } else {
+        std::cout << "FAIL: " << ret_string << " != " << CppExample::test_string << std::endl;
+        return 1;
+    }
+}