This adds support for the fstat syscall on pipe fds. Not all of the fields of struct stat are set properly (for example the access time field, inode field, etc), but it is enough for python's subprocess.run() to work correctly. Shadow logs a warning in any case.

Linux installs two different struct stat structures, one in "asm/stat.h" and the other in "asm-generic/stat.h". I think "asm/stat.h" is the right one.

Closes #3319.

processes:
- path: python3
  args: -c 'import subprocess; print(subprocess.run(["ls", "-l", "/dev/null"], capture_output=True).stdout)'
  start_time: 1

b'crw-rw-rw-. 1 nobody nobody 1, 3 Jun 23  2024 /dev/null\n'