On OpenBSD, malloc introspection (e.g., malloc_usable_size or
malloc_size) is not provided by the platform allocator. Since allocator
introspection is currently a load-bearing piece of functionality for
ManagedBuffer and ManagedBufferPointer, pending any API changes, as a
stopgap measure, this commit marks methods in ManagedBuffer and
ManagedBufferPointer calling _swift_stdlib_malloc_size and methods
dependent thereon unavailable on OpenBSD.
This may induce some compatibility issues for some files, but at least
this change ensures that we can get stdlib to build on this platform
until the evolution process addresses this problem more thoroughly.
They were never really useful to users, because their APIs were
insufficiently public. They have been replaced with a single class,
ManagedBuffer<Value,Element>, which is really designed for user
consumption.
Swift SVN r22636
