[PATCH] libstdc++: Add C++2a synchronization support

[Jonathan Wakely]

On 26/10/20 14:48 -0700, Thomas Rodgers wrote:
>+#include <ext/numeric_traits.h>
>+
>+#if __has_include(<semaphore.h>)
>+#define _GLIBCXX_HAVE_POSIX_SEMAPHORE 1
>+#include <semaphore.h>

It occurs to me now that this check probably isn't robust enough. For
any POSIX system it's probably safe to assume that <semaphore.h> means
the POSIX header and so sem_t is available.

But on non-POSIX systems there could be some other, unrelated header
called <semaphore.h> in the include paths that the user is compiling
this header with. It's not inconceivable that the user's own project
or some third party lib could provide a file called semaphore.h, which
wouldn't define sem_t, sem_init etc.

It's OK for now, but we should revisit this and add an autoconf check
for sem_init etc. to check at build time whether we've got POSIX
semaphores available or not.

Please add a "FIXME: replace this with an autoconf check" comment
here.

OK for trunk with that change, thanks.