tests/libc_newlib: add test for newlib-nano inclusion

This test verifies that when used, newlib-nano is correctly included, both
header and also linked.

tests/libc_newlib/Makefile

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+include ../Makefile.tests_common
+
+TEST_ON_CI_WHITELIST += all
+USEMODULE += embunit
+
+include $(RIOTBASE)/Makefile.include
+
+test:
+	tests/01-run.py

tests/libc_newlib/README.md

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+About
+=====
+
+Terifies if newlib/newlib-nano is correctly included by the build system
+
+At compile time, it checks that:
+
+* newlib-nano header is used when 'newlib-nano' module is included
+  * It defines `_NANO_FORMATTED_IO` macro
+    https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=newlib/newlib.hin;h=eadafc8a6a51ef7674c004a14777f6a4619115ee;hb=d34336767e45ee801ebb107e40abe4b1acbd3d14#l83
+
+At runtime, it checks that:
+
+* newlib or newlib-nano is properly linked
+  * `iprintf` is the same as `printf` or not as mentionned in:
+    https://github.com/32bitmicro/newlib-nano-1.0/blob/f157c994b9a2c4bd8d0cfe9fe8fdd9cd54f8c63b/newlib/README.nano#L32
+
+
+Without newlib, the test does nothing.

tests/libc_newlib/main.c

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+/*
+ * Copyright (C) 2018 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       Test application for newlib/newlib-nano inclusion
+ *
+ * @author      Gaëtan Harter <gaetan.harter@fu-berlin.de>
+ *
+ * @}
+ */
+
+/*
+ * Make some different functions visible between newlib and newlib-nano
+ */
+#define _DEFAULT_SOURCE 1
+
+#include <stdio.h>
+#include "embUnit.h"
+
+
+#ifdef MODULE_NEWLIB
+#include <newlib.h>
+
+/* Newlib-nano defines the _NANO_FORMATTED_IO macro
+ *
+ * Source:
+ *
+ * https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=newlib/newlib.hin;h=eadafc8a6a51ef7674c004a14777f6a4619115ee;hb=d34336767e45ee801ebb107e40abe4b1acbd3d14#l83
+ */
+#ifdef MODULE_NEWLIB_NANO
+#ifndef _NANO_FORMATTED_IO
+#error newlib-nano is enabled but the header is not visible by the build system
+#endif /* _NANO_FORMATTED_IO */
+#endif /* MODULE_NEWLIB_NANO */
+
+#endif /* MODULE_NEWLIB */
+
+
+/* Newlib-nano removed the integer only 'iprintf' functions which are now mapped
+ * to printf.
+ *
+ * Source:
+ *
+ * https://github.com/32bitmicro/newlib-nano-1.0/blob/f157c994b9a2c4bd8d0cfe9fe8fdd9cd54f8c63b/newlib/README.nano#L32
+ *
+ */
+static void test_newlib(void)
+{
+#ifdef MODULE_NEWLIB
+#ifdef MODULE_NEWLIB_NANO
+    /* Nano maps iprintf to printf */
+    TEST_ASSERT(iprintf == printf);
+#else
+    /* Normal newlib does not */
+    TEST_ASSERT(iprintf != printf);
+#endif
+#endif
+}
+
+
+static Test *tests_newlib(void)
+{
+    EMB_UNIT_TESTFIXTURES(fixtures) {
+        new_TestFixture(test_newlib),
+    };
+
+    EMB_UNIT_TESTCALLER(tests, NULL, NULL, fixtures);
+    return (Test *)&tests;
+}
+
+int main(void)
+{
+    puts("Newlib/nano test");
+    TESTS_START();
+    TESTS_RUN(tests_newlib());
+    TESTS_END();
+
+    return 0;
+}

tests/libc_newlib/tests/01-run.py

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+#!/usr/bin/env python3
+
+# Copyright (C) 2018 Freie Universität Berlin
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
+import os
+import sys
+
+
+def testfunc(child):
+    child.expect(r"OK \([0-9]+ tests\)")
+
+
+if __name__ == "__main__":
+    sys.path.append(os.path.join(os.environ['RIOTTOOLS'], 'testrunner'))
+    from testrunner import run
+    sys.exit(run(testfunc))