[PATCH] D12354: [libcxx] Add global assertion handler for debug mode.

[Duncan P. N. Exon Smith via cfe-commits]

> On 2016-Jan-21, at 17:59, Eric Fiselier <eric at efcs.ca> wrote:
> 
> EricWF added a comment.
> 
> In http://reviews.llvm.org/D12354#331776, @dexonsmith wrote:
> 
>> This patch looks correct to me.  Is there any reason it wasn't committed?
> 
> 
> I was concerned about using a function-local static in the library headers, I don't think libc++ does that anywhere else and I wanted to make sure it was safe to do.
> 
> 
> http://reviews.llvm.org/D12354

Ah, in the testing hook.  I feel like it's better than the current
situation, anyway.  Unless we have ABI guarantees for _LIBCPP_DEBUG
since this could lock us in somehow.  (Do we?  Should we?)

Thinking through a couple of other options:

 2. The test could provide its own version of _LIBCPP_ASSERT.  It's
    not obvious how to hook into the assertions in src/debug.cpp
    though.

 3. We could move __debug_assert() and __debug_assertion_handler()
    to the dylib (and use a static global variable there).

Maybe (3) is the best.  Is it important for these functions to be
inline, given that they're in the slow path anyway?