Don't crash on attempts to synthesize an invalid property.
rdar://problem/10904479

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151089 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaObjCProperty.cpp b/lib/Sema/SemaObjCProperty.cpp
index f9c064d..5df214f 100644
--- a/lib/Sema/SemaObjCProperty.cpp
+++ b/lib/Sema/SemaObjCProperty.cpp
@@ -1777,6 +1777,7 @@
           Attributes & ObjCDeclSpec::DQ_PR_copy ? "copy" : "retain (or strong)");
     Attributes &= ~(ObjCDeclSpec::DQ_PR_weak   | ObjCDeclSpec::DQ_PR_copy |
                     ObjCDeclSpec::DQ_PR_retain | ObjCDeclSpec::DQ_PR_strong);
+    PropertyDecl->setInvalidDecl();
   }
 
   // Check for more than one of { assign, copy, retain }.