Revert "Cygwin: pipe: Restore blocking mode for cygwin process at sta…

…rtup."

When Git for Windows upgraded its MSYS2 runtime from v3.3.* to v3.4.* at
long last, the t3701-add-interactive test of Git's test suite started to
hang consistently, timing out.

The culprit is a `git add -p` call that wants to read from a diff
filter. This diff filter is `cat.exe`, i.e. nothing special, but that
diff filter gets input that is larger than the pipe buffer, and
therefore must not block. Yet that is exactly what it does.

This was a regression that introduced by upgrading from MSYS2 runtime
v3.3.*. After a tedious, multi-day bisection session, the commit
introducing that regression was identified as 9078882 (Cygwin: pipe:
Restore blocking mode for cygwin process at startup., 2021-11-17), which
we hereby revert.

So what bug does this reversion reintroduce?

The commit seems to have been in response to
https://inbox.sourceware.org/cygwin/CAEv6GOB8PXHgHoz7hdJy6Bia2GWEmUDnTd252gTGinz2vuv=hA@mail.gmail.com/
which reported a bug when a C# program writes 0-byte content to a Cygwin
pipe. (Irony of ironies, this report originated from Git's realm, over
at git-ecosystem/git-credential-manager#509.)

The analysis revealed, back in December '21, that a `CYGWIN=pipe_byte`
would work around the bug, too, but that did not fix the regression in
Git's test suite.

That leaves us with the somewhat unsatisfying conclusion that we _might_
reintroduce a regression when Git Credential Manager tries to talk to an
_MSYS_ `git.exe`. But since we do not need that in Git for Windows, and
since we need to have CI builds that do not time out after 6h causing
failures, it is better to revert that commit, and in the hopefully
unlikely event that this causes _other_ problems in Git for Windows'
ecosystem, we will simply have to revisit this issue in more depth.

This fixes git-for-windows/git#4422.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

winsup/cygwin/dtable.cc

@@ -410,9 +410,6 @@ dtable::init_std_file_from_handle (int fd, HANDLE handle)
 	{
 	  fhandler_pipe *fhp = (fhandler_pipe *) fh;
 	  fhp->set_pipe_buf_size ();
-	  /* Set read pipe always to nonblocking */
-	  fhp->set_pipe_non_blocking (fhp->get_device () == FH_PIPER ?
-				      true : fhp->is_nonblocking ());
 	}
 
       if (!fh->open_setup (openflags))