Fix fstat() emulation on Windows with standard streams

The emulation of fstat() in win32stat.c caused two issues with the
existing in-core callers, failing on EINVAL when using a stream as
argument:
- psql's \copy would crash when using a stream.
- pg_recvlogical would fail with -f -.

The tests in copyselect.sql from the main test suite covers the first
case, and there is a TAP test for the second case.  However, in both
cases, as the standard streams are always redirected, automated tests
did not notice those issues, requiring a terminal on Windows to be
reproducible.

This issue has been introduced in bed9075, and the origin of the problem
is that GetFileInformationByHandle() does not work directly on streams,
so this commit adds an extra code path to emulate and return a set of
stats that match best with the reality.  Note that redirected streams
rely on handles that can be queried with GetFileInformationByHandle(),
but we can rely on GetFinalPathNameByHandleA() to detect this case.

Author: Dmitry Koval, Juan José Santamaría Flecha
Discussion: https://postgr.es/m/17288-6b58a91025a8a8a3@postgresql.org
Backpatch-through: 14

src/port/win32stat.c

@@ -289,6 +289,7 @@ int
 _pgfstat64(int fileno, struct stat *buf)
 {
 	HANDLE		hFile = (HANDLE) _get_osfhandle(fileno);
+	char		path[MAX_PATH];
 
 	if (hFile == INVALID_HANDLE_VALUE || buf == NULL)
 	{
@@ -296,6 +297,25 @@ _pgfstat64(int fileno, struct stat *buf)
 		return -1;
 	}
 
+	/*
+	 * Check if the fileno is a data stream.  If so, unless it has been
+	 * redirected to a file, getting information through its HANDLE will fail,
+	 * so emulate its stat information in the most appropriate way and return
+	 * it instead.
+	 */
+	if ((fileno == _fileno(stdin) ||
+		 fileno == _fileno(stdout) ||
+		 fileno == _fileno(stderr)) &&
+		GetFinalPathNameByHandleA(hFile, path, MAX_PATH, VOLUME_NAME_NT) == 0)
+	{
+		memset(buf, 0, sizeof(*buf));
+		buf->st_mode = _S_IFCHR;
+		buf->st_dev = fileno;
+		buf->st_rdev = fileno;
+		buf->st_nlink = 1;
+		return 0;
+	}
+
 	/*
 	 * Since we already have a file handle there is no need to check for
 	 * ERROR_DELETE_PENDING.