Fix a syntax error when ((...)) is combined with redirections (#68)

This bugfix was backported from ksh93v- 2013-10-10-alpha.

src/cmd/ksh93/sh/parse: item():
- The done label is placed after the 'inout' call for handling I/O
  redirections. This causes the command below to produce a syntax
  error because the '>' is not handled as a redirection operator
  after 'goto done':
  $ ((1+2)) > /dev/null
  /usr/bin/ksh: syntax error: `>' unexpected
  Moving the done label fixes the syntax error as 'inout' is now
  called to handle the redirection operator.

src/cmd/ksh93/tests/arith.sh:
- Add a simple regression test.

NEWS

@@ -12,6 +12,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
 - Fixed a memory leak when restoring PATH when temporarily setting PATH
   for a command (e.g. PATH=/foo/bar command ...) or in a virtual subshell.
 
+- Combining ((...)) with redirections no longer causes a syntax error
+  due to the parser handling '>' incorrectly.
+
 2020-07-07:
 
 - Four of the date formats accepted by 'printf %()T' have had their

src/cmd/ksh93/sh/parse.c

@@ -1367,13 +1367,13 @@ static Shnode_t	*item(Lex_t *lexp,int flag)
 		return(t);
 	}
 	sh_lex(lexp);
-	/* redirection(s) following a compound command */
+done:
+	/* redirection(s) following a compound command or arithmetic expression */
 	if(io=inout(lexp,io,0))
 	{
 		t=makeparent(lexp,TSETIO,t);
 		t->tre.treio=io;
 	}
-done:
 	lexp->lasttok = savwdval;
 	lexp->lastline = savline;
 	return(t);

src/cmd/ksh93/tests/arith.sh

@@ -761,4 +761,9 @@ x=0x1.0000000000000000000000000000p+6
 v=$(printf $'%.28a\n' 64)
 [[ $v == "$x" ]] || err_exit "'printf %.28a 64' failed -- expected '$x', got '$v'"
 
+# ======
+# Redirections with ((...)) should not cause a syntax error
+(eval '((1)) >/dev/null') 2>/dev/null || err_exit 'redirections with ((...)) yield a syntax error'
+
+# ======
 exit $((Errors<125?Errors:125))