cmd/compile/internal/syntax: better error recovery after missing type

R=go1.11.

This is just a copy of the fix for #23434:
https://go-review.googlesource.com/c/go/+/87898.

Test pending test harness for the syntax package.

Change-Id: I52409aebe13ec784ddd7e41190a81c7e126bdd0c
Reviewed-on: https://go-review.googlesource.com/87901Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/syntax/parser.go

@@ -1036,7 +1036,7 @@ func (p *parser) type_() Expr {
 	if typ == nil {
 		typ = p.bad()
 		p.syntax_error("expecting type")
-		p.advance()
+		p.advance(_Comma, _Colon, _Semi, _Rparen, _Rbrack, _Rbrace)
 	}
 
 	return typ