commit 272871b658429a2da4c28ddecbfbe7574f781a7f
author Eric Fiselier <eric@efcs.ca> Wed Jan 16 01:51:12 2019 +0000
committer Eric Fiselier <eric@efcs.ca> Wed Jan 16 01:51:12 2019 +0000
tree ecdc6cada1d038ba587b7c1e006e6c34b2b2e7d1
parent a8b9f59e8caf378d56e8bfcecdb22184cdabf42d

Move internal usages of `alignof`/`__alignof` to use `_LIBCPP_ALIGNOF`. 

Summary:
Starting in Clang 8.0 and GCC 8.0, `alignof` and `__alignof` return different values in same cases. Specifically `alignof` and `_Alignof` return the minimum alignment for a type, where as `__alignof` returns the preferred alignment. libc++ currently uses `__alignof` but means to use `alignof`. See  llvm.org/PR39713

This patch introduces the macro `_LIBCPP_ALIGNOF` so we can control which spelling gets used.

This patch does not introduce any ABI guard to provide the old behavior with newer compilers. However, if we decide that is needed, this patch makes it trivial to implement.

I think we should commit this change immediately, and decide what we want to do about the ABI afterwards. 

Reviewers: ldionne, EricWF

Reviewed By: ldionne, EricWF

Subscribers: jyknight, christof, libcxx-commits

Differential Revision: https://reviews.llvm.org/D54814

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@351289 91177308-0d34-0410-b5e6-96231b3b80d8