Bug#10777 ERROR File = sql_lex.cc, Line = 93 The identifier "symbols" is undefined.

 - Protect againt empty/corrupt lex_hash-h by writing output from gen_lex_hash to 
   a temporary file first.

sql/Makefile.am

@@ -142,7 +142,8 @@ sql_yacc.o:	sql_yacc.cc sql_yacc.h $(HEADERS)
 # this avoid the rebuild of the built files in a source dist
 lex_hash.h:	gen_lex_hash.cc lex.h
 		$(MAKE) $(AM_MAKEFLAGS) gen_lex_hash$(EXEEXT)
-		./gen_lex_hash$(EXEEXT) > $@
+		./gen_lex_hash$(EXEEXT) > $@-t
+		$(MV) $@-t $@
 
 # For testing of udf_example.so;  Works on platforms with gcc
 # (This is not part of our build process but only provided as an example)