fix(esp_libc): provide picolibc timespec_get

The Picolibc headers in the ESP-IDF v6.0 toolchain declare the C11
timespec_get API, but the corresponding archives do not define it.
Provide the missing compatibility implementation through esp_libc
and cover valid and invalid time bases.

components/esp_libc/CMakeLists.txt

@@ -77,6 +77,7 @@ else()
     list(APPEND srcs
          "src/picolibc/picolibc_init.c"
          "src/picolibc/rand.c"
+         "src/picolibc/timespec_get.c"
          "src/picolibc/open_memstream.c"
          "src/picolibc/errno.c"
          "src/picolibc/bufio_setvbuf.c") # TODO IDF-15494: remove this and the following lines

components/esp_libc/src/picolibc/timespec_get.c

@@ -0,0 +1,15 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <time.h>
+
+int timespec_get(struct timespec *ts, int base)
+{
+    if (base != TIME_UTC || clock_gettime(CLOCK_REALTIME, ts) < 0) {
+        return 0;
+    }
+    return base;
+}

components/esp_libc/test_apps/newlib/main/test_time.c

@@ -548,6 +548,17 @@ TEST_CASE("test posix_timers clock_... functions", "[newlib]")
     test_posix_timers_clock();
 }
 
+TEST_CASE("timespec_get returns UTC time", "[newlib]")
+{
+    struct timespec ts = {0};
+
+    TEST_ASSERT_EQUAL_INT(TIME_UTC, timespec_get(&ts, TIME_UTC));
+    TEST_ASSERT_GREATER_OR_EQUAL_INT64(0, ts.tv_sec);
+    TEST_ASSERT_GREATER_OR_EQUAL_INT32(0, ts.tv_nsec);
+    TEST_ASSERT_LESS_THAN_INT32(1000000000L, ts.tv_nsec);
+    TEST_ASSERT_EQUAL_INT(0, timespec_get(&ts, -1));
+}
+
 #define TEST_USE_CPU_CYCLES 1
 #if TEST_USE_CPU_CYCLES && CONFIG_ESP_SYSTEM_SINGLE_CORE_MODE
 #include "esp_cpu.h"