produce a more informative error message when parsing _Complex

tccgen.c

@@ -4533,6 +4533,8 @@ static int parse_btype(CType *type, AttributeDef *ad, int ignore_label)
         case TOK_BOOL:
             u = VT_BOOL;
             goto basic_type;
+        case TOK_COMPLEX:
+            tcc_error("_Complex is not yet supported");
         case TOK_FLOAT:
             u = VT_FLOAT;
             goto basic_type;

tcctok.h

@@ -45,6 +45,7 @@
      DEF(TOK_FLOAT, "float")
      DEF(TOK_DOUBLE, "double")
      DEF(TOK_BOOL, "_Bool")
+     DEF(TOK_COMPLEX, "_Complex")
      DEF(TOK_SHORT, "short")
      DEF(TOK_STRUCT, "struct")
      DEF(TOK_UNION, "union")