refactor(cxx): moved C++ init functions to cxx component

* Also fixed setting the C++ exception emergency pool size
  correctly when C++ exceptions are disabled:
  __cxx_eh_arena_size_get() is now called again even if
  CONFIG_COMPILER_CXX_EXCEPTIONS=n

components/cxx/cxx_init.cpp

@@ -0,0 +1,50 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "sdkconfig.h"
+#include "esp_log.h"
+#include "esp_private/startup_internal.h"
+
+namespace {
+    const char *TAG = "C++ init";
+}
+
+#ifdef CONFIG_COMPILER_CXX_EXCEPTIONS
+// workaround for C++ exception large memory allocation
+extern "C" void _Unwind_SetEnableExceptionFdeSorting(unsigned char enable);
+
+ESP_SYSTEM_INIT_FN(init_cxx_exceptions, SECONDARY, BIT(0), 205)
+{
+    ESP_EARLY_LOGD(TAG, "Setting C++ exception workarounds.");
+    _Unwind_SetEnableExceptionFdeSorting(0);
+    return ESP_OK;
+}
+#endif // CONFIG_COMPILER_CXX_EXCEPTIONS
+
+/**
+ * This function overwrites the same function of libsupc++ (part of libstdc++).
+ * Consequently, libsupc++ will then follow our configured exception emergency pool size.
+ *
+ * It will be called even with -fno-exception for user code since the stdlib still uses exceptions.
+ */
+extern "C" size_t __cxx_eh_arena_size_get(void)
+{
+#ifdef CONFIG_COMPILER_CXX_EXCEPTIONS
+    ESP_EARLY_LOGD(TAG, "Setting C++ exception emergency pool to %u.", CONFIG_COMPILER_CXX_EXCEPTIONS_EMG_POOL_SIZE);
+    return CONFIG_COMPILER_CXX_EXCEPTIONS_EMG_POOL_SIZE;
+#else
+    ESP_EARLY_LOGD(TAG, "Setting C++ exception emergency pool to 0.");
+    return 0;
+#endif
+}
+
+/**
+ * Dummy function used to force linking this file.
+ * This works via -u __cxx_init_dummy flag in CMakeLists.txt
+ */
+extern "C" void __cxx_init_dummy(void)
+{
+}