Correct assert text in DeclGroup::getSingleDecl()

Assert text for getSingleDecl() is inaccurate. Appears to have been copy pasted
from getDeclGroup().

Patch by Ben Taylor!

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D24518

llvm-svn: 281525

clang/include/clang/AST/DeclGroup.h

@@ -84,7 +84,7 @@ public:
   bool isDeclGroup() const { return getKind() == DeclGroupKind; }
 
   Decl *getSingleDecl() {
-    assert(isSingleDecl() && "Isn't a declgroup");
+    assert(isSingleDecl() && "Isn't a single decl");
     return D;
   }
   const Decl *getSingleDecl() const {