posix: time.h: workaround for undefined pid_t in picolibc's time.h

Define pid_t before including Picolibc's time.h, which does not yet
include the proper fix in picolibc/picolibc#1079 .

Signed-off-by: Chris Friedt <[email protected]>

Author: cfriedt

include/zephyr/posix/time.h

@@ -4,5 +4,20 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#ifndef ZEPHYR_INCLUDE_POSIX_TIME_H_
+#define ZEPHYR_INCLUDE_POSIX_TIME_H_
+
+#ifdef CONFIG_PICOLIBC
+/* temporary workaround for https://github.com/picolibc/picolibc/pull/1079 */
+#include <sys/_types.h>
+
+#ifndef _PID_T_DECLARED
+typedef __pid_t pid_t;
+#define _PID_T_DECLARED
+#endif
+#endif
+
 /* This header will soon be deprecated. Please include <time.h> instead. */
 #include_next <time.h>
+
+#endif /* ZEPHYR_INCLUDE_POSIX_TIME_H_ */