Add configure probe for rl_completion_suppress_quote.

I had supposed that all versions of Readline that have filename
quoting hooks also have the rl_completion_suppress_quote variable.
But it seems OpenBSD managed to find a version someplace that does
not, so we'll have to expend a separate configure probe for that.

(Light testing suggests that this version also lacks the bugs that
make it necessary to frob that variable.  Hooray!)

Per buildfarm.

src/bin/psql/tab-complete.c

@@ -4468,11 +4468,10 @@ complete_from_files(const char *text, int state)
 	 * anyway.  Set rl_completion_suppress_quote to prevent that.  If we do
 	 * get to quote_file_name(), we'll clear this again.  (Yes, this seems
 	 * like it's working around Readline bugs.)
-	 *
-	 * (For now, we assume that rl_completion_suppress_quote exists if the
-	 * filename quoting hooks do.)
 	 */
+#ifdef HAVE_RL_COMPLETION_SUPPRESS_QUOTE
 	rl_completion_suppress_quote = 1;
+#endif
 
 	/* If user typed a quote, force quoting (never remove user's quote) */
 	if (*text == '\'')
@@ -4842,7 +4841,9 @@ quote_file_name(char *fname, int match_type, char *quote_pointer)
 	 * on its own accord.  (This covers some additional cases beyond those
 	 * dealt with above.)
 	 */
+#ifdef HAVE_RL_COMPLETION_SUPPRESS_QUOTE
 	rl_completion_suppress_quote = 0;
+#endif
 
 	/*
 	 * If user typed a leading quote character other than single quote (i.e.,

src/include/pg_config.h.in

@@ -485,6 +485,10 @@
 /* Define to 1 if you have the `rl_completion_matches' function. */
 #undef HAVE_RL_COMPLETION_MATCHES
 
+/* Define to 1 if you have the global variable 'rl_completion_suppress_quote'.
+   */
+#undef HAVE_RL_COMPLETION_SUPPRESS_QUOTE
+
 /* Define to 1 if you have the `rl_filename_completion_function' function. */
 #undef HAVE_RL_FILENAME_COMPLETION_FUNCTION
 

src/tools/msvc/Solution.pm

@@ -332,6 +332,7 @@ sub GenerateFiles
 		HAVE_RINT                   => 1,
 		HAVE_RL_COMPLETION_APPEND_CHARACTER      => undef,
 		HAVE_RL_COMPLETION_MATCHES               => undef,
+		HAVE_RL_COMPLETION_SUPPRESS_QUOTE        => undef,
 		HAVE_RL_FILENAME_COMPLETION_FUNCTION     => undef,
 		HAVE_RL_FILENAME_QUOTE_CHARACTERS        => undef,
 		HAVE_RL_FILENAME_QUOTING_FUNCTION        => undef,