[gram.cpp] Add space before comma in bnf. (#1525)

Author: Eelis

source/preprocessor.tex

@@ -53,7 +53,7 @@
 \>\terminal{\# define}\>\>identifier replacement-list new-line\br
 \>\terminal{\# define}\>\>identifier lparen identifier-list\opt{} \terminal{)} replacement-list new-line\br
 \>\terminal{\# define}\>\>identifier lparen \terminal{... )} replacement-list new-line\br
-\>\terminal{\# define}\>\>identifier lparen identifier-list, \terminal{... )} replacement-list new-line\br
+\>\terminal{\# define}\>\>identifier lparen identifier-list \terminal{, ... )} replacement-list new-line\br
 \>\terminal{\# undef}\>\>identifier new-line\br
 \>\terminal{\# line}\>\>pp-tokens new-line\br
 \>\terminal{\# error}\>\>pp-tokens\opt new-line\br