rp2: Workaround pico_aon_timer timezone binary size increase.

Provide stub implementations of localtime_r() and mktime() to avoid
code size increase.

Reported upstream at https://github.com/raspberrypi/pico-sdk/issues/1810

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

ports/rp2/CMakeLists.txt

@@ -147,6 +147,7 @@ set(MICROPY_SOURCE_DRIVERS
 
 set(MICROPY_SOURCE_PORT
     clocks_extra.c
+    datetime_patch.c
     fatfs_port.c
     help.c
     machine_bitstream.c

ports/rp2/datetime_patch.c

@@ -0,0 +1,42 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2024 Angus Gratton
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <time.h>
+#include "py/mpconfig.h"
+#include "shared/timeutils/timeutils.h"
+
+// This is a workaround for the issue that pico-sdk datetime.c will otherwise
+// pull in a lot of libc code for time zone support.
+//
+// Upstream issue is https://github.com/raspberrypi/pico-sdk/issues/1810
+
+struct tm *localtime_r(const time_t *__restrict time, struct tm *__restrict local_time) {
+    return gmtime_r(time, local_time);
+}
+
+time_t mktime(struct tm *__restrict tm) {
+    return timeutils_mktime(tm->tm_year, tm->tm_mon, tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec);
+}