lexer: allow `-prepended identifiers to start with numerals

This is necessary to be able to cite names in some modules by explicit
module name, since module names can and do start with numerals.

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>

libdtrace/dt_lex.l

@@ -50,7 +50,7 @@ int yydebug;
 
 RGX_AGG		"@"[a-zA-Z_][0-9a-zA-Z_]*
 RGX_PSPEC	[-$:a-zA-Z_.?*\\\[\]!][-$:0-9a-zA-Z_.`?*\\\[\]!]*
-RGX_IDENT	[a-zA-Z_`][0-9a-zA-Z_`]*
+RGX_IDENT	([a-zA-Z_`][0-9a-zA-Z_`]*)|([0-9][0-9a-zA-Z_]*`[0-9a-zA-Z_`]*)
 RGX_INT		([0-9]+|0[xX][0-9A-Fa-f]+)[uU]?[lL]?[lL]?
 RGX_FP		([0-9]+("."?)[0-9]*|"."[0-9]+)((e|E)("+"|-)?[0-9]+)?[fFlL]?
 RGX_WS		[\f\n\r\t\v ]