Mark failed initializers as errors

When the initialization expression on a variable declaration fails, give it an ErrorType so Swift does not redundantly diagnose its un-inferrable type.

Fixes:

* test/NameBinding/stdlib.swift
* test/decl/typealias/protocol.swift

Would also have redundantly fixed the same tests as 2e875e7e, but the targeted solution there is cleaner.

Author: beccadax

lib/Sema/TypeCheckConstraints.cpp

@@ -2099,6 +2099,10 @@ bool TypeChecker::typeCheckBinding(Pattern *&pattern, Expr *&initializer,
                                      contextualPurpose,
                                      flags,
                                      &listener);
+  
+  if (hadError && !initializer->getType()) {
+    initializer->setType(ErrorType::get(Context));
+  }
 
   if (hadError && !pattern->hasType()) {
     pattern->setType(ErrorType::get(Context));