feat(libc): pass __PICOLIBC_ERRNO_FUNCTION to picolibc builds

components/esp_libc/src/picolibc/errno.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2025-2026 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -12,11 +12,10 @@
  * 'errno' is defined in the TDATA section. The linker script ensures that
  * it is positioned at the beginning of the TDATA segment.
  */
+#undef errno
 __thread int errno __attribute__((section(".tdata.errno"))) = 0;
 
-#if CONFIG_LIBC_PICOLIBC_NEWLIB_COMPATIBILITY
 int *__errno(void)
 {
     return &errno;
 }
-#endif