[Serialization] Recover if a typealias's underlying type is broken (#12979)

We could handle a typealias itself disappearing, but not if the
typealias was okay but the underlying type wasn't. This came up in
real Swift 3/4 mix-and-match code.

rdar://problem/34940079

include/swift/Serialization/ModuleFormat.h

@@ -54,7 +54,7 @@ const uint16_t VERSION_MAJOR = 0;
 /// in source control, you should also update the comment to briefly
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
-const uint16_t VERSION_MINOR = 386; // Last change: @callee_guaranted closures
+const uint16_t VERSION_MINOR = 387; // Last change: dependencies for typealiases
 
 using DeclIDField = BCFixed<31>;
 
@@ -819,7 +819,8 @@ namespace decls_block {
     TypeIDField, // interface type (no longer used)
     BCFixed<1>,  // implicit flag
     GenericEnvironmentIDField, // generic environment
-    AccessLevelField // access level
+    AccessLevelField, // access level
+    BCArray<TypeIDField> // dependency types
     // Trailed by generic parameters (if any).
   >;