newlib: add C++ guards to the platform-specific dirent.h

Before newlib 3.3.0, <dirent.h> bundled in newlib did not include any
function declarations. Instead, the file included the platform-
specific <sys/dirent.h>. This inclusion was inside a C++ guard block.
ESP-IDF provided sys/dirent.h inside newlib component, and this file
contained all the necessary function and structure declarations.

Since https://github.com/espressif/newlib-esp32/commit/da418955f5dca2f8570561c5dd6e79e25ebaeba2,
common function declarations have been added to <dirent.h> in newlib.
However, the inclusion of sys/dirent.h has been moved out of the C++
guard block. However we didn't notice this change and did not update
sys/dirent.h in ESP-IDF newlib component to and the now-required
C++ guards there.

This commit adds the missing C++ guards to the platform-specific
sys/dirent.h.

The declarations of common dirent.h functions are now present both in
<dirent.h> (provided by newlib) and in sys/dirent.h (provided by IDF).
We keep the declarations in sys/dirent.h for compatibility, since some
ESP-IDF files and applications may include <sys/dirent.h> directly,
rather than <dirent.h>.

Closes https://github.com/espressif/esp-idf/issues/7204

components/newlib/platform_include/sys/dirent.h

@@ -19,11 +19,16 @@
 
 /**
  * This header file provides POSIX-compatible definitions of directory
- * access functions and related data types.
+ * access data types. Starting with newlib 3.3, related functions are defined
+ * in 'dirent.h' bundled with newlib.
  * See http://pubs.opengroup.org/onlinepubs/7908799/xsh/dirent.h.html
  * for reference.
  */
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * @brief Opaque directory structure
  */
@@ -57,3 +62,7 @@ void seekdir(DIR* pdir, long loc);
 void rewinddir(DIR* pdir);
 int closedir(DIR* pdir);
 int readdir_r(DIR* pdir, struct dirent* entry, struct dirent** out_dirent);
+
+#ifdef __cplusplus
+}
+#endif

tools/ci/check_public_headers_exceptions.txt

@@ -30,8 +30,6 @@ components/lwip/include/apps/dhcpserver/dhcpserver.h
 
 components/lwip/lwip/src/include/lwip/priv/memp_std.h
 
-components/vfs/include/sys/dirent.h
-
 components/esp_phy/esp32/include/phy_init_data.h
 
 components/spi_flash/include/spi_flash_chip_issi.h