Add implementations of sprintf and snprintf so that we can get a bit
closer to compiling libc-test.

Merge the final components for Aarch64 support into master.

Dan Robertson authored 7 years ago and Dan Robertson committed 7 years ago

Don't use syscalls that are non-existent on Aarch64 linux boxes. The
FORK and RMDIR syscalls are no longer present and the CLONE and UNLINKAT
syscalls are used instead.

The current implementation of open requires the user to pass all three
args to the function. It should use a va_list and allow a user to
provide only the filename and flags.

Wrote tests for the functions implemented in 40558b26 and maybe made that
test a little more comprehensible.

Also made sure that fmt.sh and test.sh were being executed by bash all
the time (compatibility with other shells).