tcc -E: fix pasting empty tokens
tcc -E: fix pasting empty tokens

/* test case */
#define t(x,y,z) x ## y ## z
int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
        t(10,,), t(,11,), t(,,12), t(,,) };

tcc -E: xpected result:
int j[] = { 123, 45, 67, 89,
 10, 11, 12, };

Archs/TinyCC,leeduhem/tinycc,mitake/tinycc,acook/tinycc,avih/tinycc,gfwilliams/tinycc,fstudio/tinycc,andreiw/tinycc,soywiz/tinycc,Wallbraker/DCPU-TCC,rchandramouli/tinycc,shinh/nacltcc,melkior/tinycc,yousong/tinycc,fstudio/tinycc,code4game/tinycc,seyko2/tinycc,soywiz/tinycc,andrewchambers/tccmirror,melkior/tinycc,metaeducation/tcc,rchandramouli/tinycc,fstudio/tinycc,metaeducation/tcc,alfonsokim/tinycc,yousong/tinycc,mobiphil/tinnycc,shinh/nacltcc,alfonsokim/tinycc,seyko2/tinycc,melkior/tinycc,mirror/tinycc,alfonsokim/tinycc,metaeducation/tcc,Saectar/inherpreter,mirror/tinycc,seyko2/tinycc,rchandramouli/tinycc,leeduhem/tinycc,rchandramouli/tinycc,acook/tinycc,FriedBreakfast/tcc,avih/tinycc,run4flat/tinycc,andrewchambers/tccmirror,acook/tinycc,run4flat/tinycc,andrewchambers/tccmirror,ftdi-paul-jiao/tinyCC,mirror/tinycc,mingodad/tinycc,gfwilliams/tinycc,Saectar/inherpreter,alfonsokim/tinycc,avih/tinycc,xcm/tcc,soywiz/tinycc,seyko2/tinycc,ftdi-paul-jiao/tinyCC,ftdi-paul-jiao/tinyCC,FriedBreakfast/tcc,mobiphil/tinnycc,leeduhem/tinycc,FriedBreakfast/tcc,Archs/TinyCC,gfwilliams/tinycc,Saectar/inherpreter,avih/tinycc,gfwilliams/tinycc,shinh/nacltcc,Archs/TinyCC,fstudio/tinycc,xcm/tcc,run4flat/tinycc,alfonsokim/tinycc,mirror/tinycc,shinh/nacltcc,fstudio/tinycc,code4game/tinycc,mobiphil/tinnycc,Wallbraker/DCPU-TCC,shinh/nacltcc,seyko2/tinycc,gfwilliams/tinycc,mingodad/tinycc,andreiw/tinycc,acook/tinycc,xcm/tcc,run4flat/tinycc,melkior/tinycc,leeduhem/tinycc,run4flat/tinycc,FriedBreakfast/tcc,Archs/TinyCC,andrewchambers/tccmirror,mitake/tinycc,mitake/tinycc,Archs/TinyCC,yousong/tinycc,melkior/tinycc,yousong/tinycc,Saectar/inherpreter,mobiphil/tinnycc,leeduhem/tinycc,rchandramouli/tinycc,FriedBreakfast/tcc,code4game/tinycc,metaeducation/tcc,mitake/tinycc,metaeducation/tcc,ftdi-paul-jiao/tinyCC,Wallbraker/DCPU-TCC,mingodad/tinycc,soywiz/tinycc,Saectar/inherpreter,andrewchambers/tccmirror,mingodad/tinycc,andreiw/tinycc