Throw internal error on calling dummy built-in (re: c5018f7)

It's best for the temporary parse-time dummy built-in not to simply
call b_true() but to actually give an "internal error" message, as
it is never supposed to be called.

src/cmd/ksh93/bltins/typeset.c

@@ -249,7 +249,7 @@ int    b_typeset(int argc,char *argv[],Shbltin_t *context)
 			new_argv[1] = "-n";
 		else
 		{
-			errormsg(SH_DICT, ERROR_exit(128), "internal error");
+			errormsg(SH_DICT, ERROR_PANIC, e_internal);
 			UNREACHABLE();
 		}
 		for (n = 1; n <= argc; n++)

src/cmd/ksh93/data/msg.c

@@ -129,6 +129,7 @@ const char e_badrange[]		= "%d-%d: invalid range";
 const char e_eneedsarg[]	= "-e - requires single argument";
 const char e_limit[]		= "%s: could not get limit";
 const char e_overlimit[]	= "%s: limit exceeded";
+const char e_internal[]		= "internal error";
 const char e_badsyntax[]	= "incorrect syntax";
 const char e_badwrite[]		= "write to %d failed";
 const char e_staticfun[]	= "%s: defined as a static function in type %s and cannot be redefined";

src/cmd/ksh93/include/builtins.h

@@ -125,6 +125,7 @@ extern const char	e_notimp[];
 extern const char	e_nosupport[];
 extern const char	e_limit[];
 extern const char	e_overlimit[];
+extern const char	e_internal[];
 
 extern const char	e_eneedsarg[];
 extern const char	e_oneoperand[];

src/cmd/ksh93/sh/parse.c

@@ -164,6 +164,15 @@ static void typeset_order(const char *str,int line)
 	}
 }
 
+static int b_dummy(int argc, char *argv[], Shbltin_t *context)
+{
+	NOT_USED(argc);
+	NOT_USED(argv[0]);
+	NOT_USED(context);
+	errormsg(SH_DICT,ERROR_PANIC,e_internal);
+	UNREACHABLE();
+}
+
 /*
  * This function handles linting for 'typeset' options via typeset_order().
  *
@@ -233,7 +242,7 @@ static void check_typedef(struct comnod *tp, char intypeset)
 			dcl_tree = dtopen(&_Nvdisc, Dtoset);
 			dtview(sh.bltin_tree, dcl_tree);
 		}
-		nv_onattr(sh_addbuiltin(cp, b_true, NULL), NV_BLTIN|BLT_DCL);
+		nv_onattr(sh_addbuiltin(cp, b_dummy, NULL), NV_BLTIN|BLT_DCL);
 	}
 }
 /*