Fix lstat() for broken junction points on Windows.

When using junction points to emulate symlinks on Windows, one edge case
was not handled correctly by commit c5cb8f3b: if a junction point is
broken (pointing to a non-existent path), we'd report ENOENT.  This
doesn't break any known use case, but was noticed while developing a
test suite for these functions and is fixed here for completeness.

Also add translation ERROR_CANT_RESOLVE_FILENAME -> ENOENT, as that is
one of the errors Windows can report for some kinds of broken paths.

Discussion: https://postgr.es/m/CA%2BhUKG%2BajSQ_8eu2AogTncOnZ5me2D-Cn66iN_-wZnRjLN%2Bicg%40mail.gmail.com
(cherry picked from commit 387803d81d)

Author: Thomas Munro <tmunro@postgresql.org>
Author: Alexandra Wang <alexandra.wang.oss@gmail.com>

src/port/win32error.c

@@ -164,6 +164,12 @@ static const struct
 	},
 	{
 		ERROR_DELETE_PENDING, ENOENT
+	},
+	{
+		ERROR_INVALID_NAME, ENOENT
+	},
+	{
+		ERROR_CANT_RESOLVE_FILENAME, ENOENT
 	}
 };
 

src/port/win32stat.c

@@ -127,15 +127,30 @@ _pglstat64(const char *name, struct stat *buf)
 
 	hFile = pgwin32_open_handle(name, O_RDONLY, true);
 	if (hFile == INVALID_HANDLE_VALUE)
+	{
+		if (errno == ENOENT)
+		{
+			/*
+			 * If it's a junction point pointing to a non-existent path, we'll
+			 * have ENOENT here (because pgwin32_open_handle does not use
+			 * FILE_FLAG_OPEN_REPARSE_POINT).  In that case, we'll try again
+			 * with readlink() below, which will distinguish true ENOENT from
+			 * pseudo-symlink.
+			 */
+			memset(buf, 0, sizeof(*buf));
+			ret = 0;
+		}
+		else
 			return -1;
-
+	}
+	else
 		ret = fileinfo_to_stat(hFile, buf);
 
 	/*
 	 * Junction points appear as directories to fileinfo_to_stat(), so we'll
 	 * need to do a bit more work to distinguish them.
 	 */
-	if (ret == 0 && S_ISDIR(buf->st_mode))
+	if ((ret == 0 && S_ISDIR(buf->st_mode)) || hFile == INVALID_HANDLE_VALUE)
 	{
 		char		next[MAXPGPATH];
 		ssize_t		size;
@@ -171,9 +186,11 @@ _pglstat64(const char *name, struct stat *buf)
 			buf->st_mode &= ~S_IFDIR;
 			buf->st_mode |= S_IFLNK;
 			buf->st_size = size;
+			ret = 0;
 		}
 	}
 
+	if (hFile != INVALID_HANDLE_VALUE)
 		CloseHandle(hFile);
 	return ret;
 }