tccpp.c: Fix failing `PPTest 03` by reverting rogue modification in `macro_arg_subst`
tccpp.c: Fix failing `PPTest 03` by reverting rogue modification in `macro_arg_subst`

code4game/tinycc,metaeducation/tcc,andreiw/tinycc,mingodad/tinycc,andreiw/tinycc,run4flat/tinycc,mirror/tinycc,metaeducation/tcc,avih/tinycc,mingodad/tinycc,andreiw/tinycc,metaeducation/tcc,code4game/tinycc,seyko2/tinycc,run4flat/tinycc,seyko2/tinycc,run4flat/tinycc,run4flat/tinycc,mirror/tinycc,avih/tinycc,mingodad/tinycc,avih/tinycc,avih/tinycc,seyko2/tinycc,metaeducation/tcc,run4flat/tinycc,code4game/tinycc,mingodad/tinycc,mirror/tinycc,seyko2/tinycc,seyko2/tinycc,mirror/tinycc,metaeducation/tcc