Make sure real __stdio_exit() is called on exit and not the dummy noop
versions. This fixes the issue of truncated output when redirecting
output to a file or pipe. It also fixes truncated output on programs
that forget to call fclose()
This is a workaround for an issue in which binaries compiled with our
tcc+musl toolchain can fail to write complete output when stdout is
redirected to a file or pipe.