Pass thd as an argument to yylex().

sql/sql_lex.cc:
  Pass thd as an argument to yylex(), avoiding the use of current_lex
  (and thus current_thd).

sql/sql_lex.cc

@@ -442,13 +442,13 @@ inline static uint int_token(const char *str,uint length)
 // STATE_OPERATOR_OR_IDENT ; last state was an ident, text or number
 // 			     (which can't be followed by a signed number)
 
-int yylex(void *arg)
+int yylex(void *arg, void *yythd)
 {
   reg1	uchar c;
   int	tokval;
   uint length;
   enum lex_states state,prev_state;
-  LEX	*lex=current_lex;
+  LEX	*lex= &(((THD *)yythd)->lex);
   YYSTYPE *yylval=(YYSTYPE*) arg;
 
   lex->yylval=yylval;			// The global state

sql/sql_yacc.yy

@@ -17,10 +17,12 @@
 /* sql_yacc.yy */
 
 %{
-/* Pass thd as an arg to yyparse(). The type will be void*, so it
-** must be  cast to (THD*) when used. Use the YYTHD macro for this.
+/* thd is passed as an arg to yyparse(), and subsequently to yylex().
+** The type will be void*, so it must be  cast to (THD*) when used.
+** Use the YYTHD macro for this.
 */
 #define YYPARSE_PARAM yythd
+#define YYLEX_PARAM yythd
 #define YYTHD ((THD *)yythd)
 
 #define MYSQL_YACC
@@ -37,7 +39,7 @@
 #include <myisammrg.h>
 
 extern void yyerror(const char*);
-int yylex(void *yylval);
+int yylex(void *yylval, void *yythd);
 
 #define yyoverflow(A,B,C,D,E,F) if (my_yyoverflow((B),(D),(int*) (F))) { yyerror((char*) (A)); return 2; }