widl: Support WinRT mta threading attribute parsing.

tools/widl/parser.l

@@ -385,6 +385,7 @@ static const struct keyword attr_keywords[] =
 	{"marshaling_behavior",         tMARSHALINGBEHAVIOR,        1},
 	{"maybe",                       tMAYBE,                     0},
 	{"message",                     tMESSAGE,                   0},
+	{"mta" ,                        tMTA,                       0},
 	{"neutral",                     tNEUTRAL,                   0},
 	{"nocode",                      tNOCODE,                    0},
 	{"nonbrowsable",                tNONBROWSABLE,              0},

tools/widl/parser.y

@@ -222,6 +222,7 @@ static typelib_t *current_typelib;
 %token tMAYBE tMESSAGE
 %token tMETHODS
 %token tMODULE
+%token tMTA
 %token tNAMESPACE
 %token tNOCODE tNONBROWSABLE
 %token tNONCREATABLE
@@ -1154,6 +1155,7 @@ threading_type:
 	| tSINGLE				{ $$ = THREADING_SINGLE; }
 	| tFREE					{ $$ = THREADING_FREE; }
 	| tBOTH					{ $$ = THREADING_BOTH; }
+	| tMTA					{ $$ = THREADING_FREE; }
 	;
 
 pointer_type: