The delay parameter has 'int' type while explicit int32_t is used in sigtimedwait() (sig_timedwait.c) This can lead to wrong argument for systems that have default int size different than int32 (namely AVR).

time.h: Add timeradd(), timersub(), timerclear(), timerisset(), and timercmp() as macros. These are non-POSIX interfaces, but included in most BSD deriviatives, included Linux.  From Manuel Stühn

waitpid:  CRITICAL BUGFIX.  Add a reference counting mechansim to prevent wait from using stale memory that was freed by the exiting task