Add fixit hints for misplaced C++11 attributes around class specifiers.

Add fixit hints for misplaced C++11 attributes around class specifiers.

Following r168626, in class declaration or definition, there are a combination of syntactic locations
where C++11 attributes could appear, and among those the only valid location permitted by standard is
between class-key and class-name. So for those attributes appear at wrong locations, fixit is used to
move them to expected location and we recover by applying them to the class specifier.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171757 91177308-0d34-0410-b5e6-96231b3b80d8