Enforce translation mode for Windows frontends to text with open/fopen

Allowing frontends to use concurrent-safe open() and fopen() via 0ba06e0
has the side-effect of switching the default translation mode from text
to binary, so the switch can cause breakages for frontend tools when the
caller of those new versions specifies neither binary and text.  This
commit makes sure to maintain strict compatibility with past versions,
so as no frontends should see a difference when upgrading.

Author: Laurenz Albe
Reviewed-by: Michael Paquier, Tom Lane
Discussion: https://postgr.es/m/20180917140202.GF31460@paquier.xyz

src/port/open.c

@@ -71,6 +71,20 @@ pgwin32_open(const char *fileName, int fileFlags,...)
 						 _O_SHORT_LIVED | O_DSYNC | O_DIRECT |
 						 (O_CREAT | O_TRUNC | O_EXCL) | (O_TEXT | O_BINARY))) == fileFlags);
 
+#ifdef FRONTEND
+
+	/*
+	 * Since PostgreSQL 12, those concurrent-safe versions of open() and
+	 * fopen() can be used by frontends, having as side-effect to switch the
+	 * file-translation mode from O_TEXT to O_BINARY if none is specified.
+	 * Caller may want to enforce the binary or text mode, but if nothing is
+	 * defined make sure that the default mode maps with what versions older
+	 * than 12 have been doing.
+	 */
+	if ((fileFlags & O_BINARY) == 0)
+		fileFlags |= O_TEXT;
+#endif
+
 	sa.nLength = sizeof(sa);
 	sa.bInheritHandle = TRUE;
 	sa.lpSecurityDescriptor = NULL;