Documentation cleanup: escape Objective-C @keywords in Doxygen comments.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158565 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/DeclObjC.cpp b/lib/AST/DeclObjC.cpp
index f07b9e0..b6b3f7d 100644
--- a/lib/AST/DeclObjC.cpp
+++ b/lib/AST/DeclObjC.cpp
@@ -1169,7 +1169,7 @@
 }
 
 /// FindPropertyImplIvarDecl - This method lookup the ivar in the list of
-/// properties implemented in this category @implementation block and returns
+/// properties implemented in this category \@implementation block and returns
 /// the implemented property that uses it.
 ///
 ObjCPropertyImplDecl *ObjCImplDecl::
@@ -1184,8 +1184,8 @@
 }
 
 /// FindPropertyImplDecl - This method looks up a previous ObjCPropertyImplDecl
-/// added to the list of those properties @synthesized/@dynamic in this
-/// category @implementation block.
+/// added to the list of those properties \@synthesized/\@dynamic in this
+/// category \@implementation block.
 ///
 ObjCPropertyImplDecl *ObjCImplDecl::
 FindPropertyImplDecl(IdentifierInfo *Id) const {