fix(newlib): fix __atomic_test_and_set to ensure atomicity

Before the change described in
https://gcc.gnu.org/pipermail/gcc-patches/2023-September/631393.html it
appeared that inlining built-in GCC function __atomic_test_and_set() was
incorrect. It resulted in a non-atomic write.
For GCC toolchains which do not have such patch yet, this commit fixes
__atomic_test_and_set to be atomic in IDF's builds.

components/newlib/platform_include/stdatomic.h

@@ -0,0 +1,24 @@
+/*
+ * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#pragma once
+#include_next "stdatomic.h"
+#ifndef __clang__
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static inline bool __atomic_test_and_set(volatile void *ptr, int memorder)
+{
+    return __atomic_exchange_1((bool *)ptr, true, memorder);
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

components/newlib/test_apps/main/test_stdatomic.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2022-2025 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Unlicense OR CC0-1.0
  */
@@ -10,6 +10,7 @@
 #include <stdatomic.h>
 #include <stdio.h>
 #include <pthread.h>
+#include "esp_heap_caps.h"
 #include "unity.h"
 #include "unity_fixture.h"
 
@@ -30,6 +31,18 @@ TEST_TEAR_DOWN(stdatomic)
 {
 }
 
+TEST(stdatomic, test_atomic_flag)
+{
+    bool x8 = 0;
+
+    x8 = atomic_flag_test_and_set(&g_atomic8);
+    TEST_ASSERT_EQUAL_HEX8(0x00, x8);
+    TEST_ASSERT_EQUAL_HEX8(0x01, g_atomic8);
+    atomic_flag_clear(&g_atomic8);
+    TEST_ASSERT_EQUAL_HEX8(0x00, g_atomic8);
+}
+
+
 TEST(stdatomic, test_64bit_atomics)
 {
     unsigned long long x64 = 0;
@@ -128,6 +141,7 @@ static void* exclusion_test_task(void *varg)
 
 TEST_GROUP_RUNNER(stdatomic)
 {
+    RUN_TEST_CASE(stdatomic, test_atomic_flag)
     RUN_TEST_CASE(stdatomic, test_64bit_atomics)
     RUN_TEST_CASE(stdatomic, test_32bit_atomics)
     RUN_TEST_CASE(stdatomic, test_16bit_atomics)