And clean up various stale declarations and macros that this turned up.
In particular:
- Don't install pthread.h or aio.h in THREAD_MODEL=single mode.
- Don't define mkstemp and friends, since WASI currently has no support for
temporary directories.
Whether these are defined or not depends on the version of clang in use,
and they're not that important at this time, so for now just ignore them
for the purposes of this testing output.
This populates the repo with a very minimal set of files. This is just
enough to set out a basic outline. Hopefully as we move forward we'll
be replacing many of these parts, but this is just something basic to
get things started.
This tree isn't really usable yet, as it doesn't yet have an easy way
to obtain a compiler-rt/libgcc build.