Testsuite: open/close stdin/stdout/stderr explicitly

This allows run_command's to contain `|`, and `no_stdin` isn't necessary
anymore.

Unfortunately it doesn't fix T7037 on Windows which I had hoped it would
(testsuite driver tries to read a file that it just created itself, but
the OS says it doesn't exist).

The only drawback of this commit is that the command that the testsuite
prints to the terminal (for debugging purposes) doesn't mention the
files that stdout and stderr are redirected to anymore. This is probably
ok.

Update submodule unix.

Differential Revision: https://phabricator.haskell.org/D1234

1 files changed, 0 insertions, 0 deletions

diff --git a/libraries/unix b/libraries/unix
-Subproject 5b2e91a09190f1686ea195d25183abda1757d77
+Subproject 40820da5fb35c53aed53c211277c3e6077c1ddf