[reference-binding] Fix an ambiguity when parsing inout in function types.

This was exposed by:

decl/enum/enumtest.swift

The problem here is that we are now allowing for inout to be the start of a
swift decl. This means that if one defines an enum case with a inout parameter,
the parser gets confused and doesnt think it is part of the type. I worked
around this by changing canParseTupleTypeBody to say that an inout binding
cannot be parsed as part of a tuple type. This fits already with how we want to
model this.

Author: gottesmm

lib/Parse/ParseType.cpp

@@ -1676,7 +1676,10 @@ bool Parser::canParseOldStyleProtocolComposition() {
 
 bool Parser::canParseTypeTupleBody() {
   if (Tok.isNot(tok::r_paren) && Tok.isNot(tok::r_brace) &&
-      Tok.isNotEllipsis() && !isStartOfSwiftDecl()) {
+      Tok.isNotEllipsis() &&
+      // In types, we do not allow for an inout binding to be declared in a
+      // tuple type.
+      (Tok.is(tok::kw_inout) || !isStartOfSwiftDecl())) {
     do {
       // The contextual inout marker is part of argument lists.
       consumeIf(tok::kw_inout);