* libc/sys/rtems/sys/queue.h: New file.
* libc/include/sys/signal.h: Reflect renumbering of signals to
fit into 32-bit mask.
* libc/include/sys/unistd.h: Add fdatasync() prototype.
* libc/sys/rtems/crt0.c: Add more symbols which may be implicitly
required. In particular, add the reentrant variants of libc calls.
* libc/sys/rtems/sys/dirent.h: Add scandir() prototype.
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