fix "$-" expansion for posix option (re: 921bbcae)

In the SHOPT_BASH code, the -o posix option was given a '\374'
(0xFC, 252) single-letter option character. Reasons unclear. The
'set' builtin doesn't accept it. It can be omitted and the option
still works. And it caused the "$-" expansion (listing active
short-form options) to include that invalid high-bit character if
the -o posix option is active, which is clearly wrong.

src/cmd/ksh93/sh/args.c: optksh[], flagval[]:
- Remove '\374' one-letter option equivalent for SH_POSIX.

src/cmd/ksh93/tests/options.sh:
- Add test verifying that '-o posix' does not affect "$-".

src/cmd/ksh93/sh/args.c

@@ -54,13 +54,12 @@
 static	char		*null;
 
 /* The following order is determined by sh_optset */
-static  const char optksh[] =  PFSHOPT "\374" "DircabefhkmnpstuvxBCGEl" HFLAG;
+static  const char optksh[] =  PFSHOPT "DircabefhkmnpstuvxBCGEl" HFLAG;
 static const int flagval[]  =
 {
 #if SHOPT_PFSH
 	SH_PFSH,
 #endif
-	SH_POSIX,
 	SH_DICTIONARY, SH_INTERACTIVE, SH_RESTRICTED, SH_CFLAG,
 	SH_ALLEXPORT, SH_NOTIFY, SH_ERREXIT, SH_NOGLOB, SH_TRACKALL,
 	SH_KEYWORD, SH_MONITOR, SH_NOEXEC, SH_PRIVILEGED, SH_SFLAG, SH_TFLAG,

src/cmd/ksh93/tests/options.sh

@@ -531,4 +531,15 @@ print '. ./dotfile' > envfile
 print $'alias print=:\nprint foobar' > dotfile
 [[ $(ENV=/.$PWD/envfile $SHELL -i -c : 2>/dev/null) == foobar ]] && err_exit 'files source from profile does not process aliases correctly'
 
+# ======
+# test that '-o posix' option (not having a letter) does not affect "$-" expansion
+(
+	command set +o posix 2>/dev/null
+	opt1=$-
+	command set -o posix 2>/dev/null
+	opt2=$-
+	[[ $opt1 == "$opt2" ]]
+) || err_exit '-o posix option affects $- expansion'
+
+# ======
 exit $((Errors<125?Errors:125))