1. prctl() check is not required for host-compile on any OS due to prctl
is not used in rpcgen which is only one is compiled during host-compile
phase. prctl() check is disabled via HOST_CONFIGURE_VARS in OpenWrt makefile

2. __DARWIN_ONLY_64_BIT_INO_T is true on macos arm64 so struct stat64
and stat64() are not available. This patch defines stat64 as stat if
__DARWIN_ONLY_64_BIT_INO_T is true

Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>