[MS] Allow access to ambiguous, inaccessible direct bases

Summary:
Clang typically warns that in the following class hierarchy, 'A' is
inaccessible because there is no series of casts that the user can
write to access it unambiguously:
  struct A { };
  struct B : A { };
  struct C : A, B { };

MSVC allows the user to convert from C* to A*, though, and we've
encountered this issue in the latest Windows SDK headers.

This patch allows this conversion when -fms-compatibility is set and
adds a warning for it under -Wmicrosoft-inaccessible-base.

Reviewers: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D39389

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@316807 91177308-0d34-0410-b5e6-96231b3b80d8

0 files changed, 0 insertions, 0 deletions