SILGen: flesh out Foundation stubs further

The local bridging headers needed two new definitions:
  - NSErrorDomain
  - NS_OPTIONS

These can be used by the SILGen tests to build against a stubbed
Foundation rather than requiring the host to provide it.

Author: compnerd

test/SILGen/Inputs/usr/include/BridgeTestFoundation.h

@@ -1,6 +1,8 @@
 #import "ObjectiveC.h"
 #import "dispatch.h"
 
+#define NS_OPTIONS(type, name) type name; enum
+
 #pragma clang assume_nonnull begin
 
 @interface NSString : NSObject<NSCopying>
@@ -10,6 +12,8 @@
 
 @end
 
+typedef NSString *NSErrorDomain;
+
 @interface NSArray<ObjectType> : NSObject
 
 - (_Nonnull instancetype)initWithObjects:(const _Null_unspecified ObjectType * _Null_unspecified)objects count:(int)count;