Allow trailing commas in bare lists

This applies to macro arguments, DB, DW, DL, DS,
PRINT, PRINTLN, EXPORT, PURGE, and OPT.

It also removes support for empty entries in DB/DW/DL.
(Deprecating it would require keeping parser support,
which is ambiguous with trailing commas.)

Fixes #753

include/asm/warning.h

@@ -19,7 +19,6 @@ enum WarningID {
 	WARNING_CHARMAP_REDEF,        /* Charmap entry re-definition */
 	WARNING_DIV,		      /* Division undefined behavior */
 	WARNING_EMPTY_DATA_DIRECTIVE, /* `db`, `dw` or `dl` directive without data in ROM */
-	WARNING_EMPTY_ENTRY,	      /* Empty entry in `db`, `dw` or `dl` */
 	WARNING_EMPTY_MACRO_ARG,      /* Empty macro argument */
 	WARNING_EMPTY_STRRPL,	      /* Empty second argument in `STRRPL` */
 	WARNING_LARGE_CONSTANT,	      /* Constants too large */