In Microsoft mode, allow pure specifier (=0) on inline functions declared at class...

In Microsoft mode, allow pure specifier (=0) on inline functions declared at class scope.
This removes 2 errors when parsing MFC code with clang

Example:
class A {
    virtual void f() = 0 { }
}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@131175 91177308-0d34-0410-b5e6-96231b3b80d8