[patch] libstdc++/64847 add autoconf checks for pthread_rwlock_t

[Jonathan Wakely]

On 12/03/15 18:49 +0000, Jonathan Wakely wrote:
>I assumed that Pthreads was enough to ensure pthread_rwlock_t but
>https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64847 shows that isn't
>true for HPUX (seems it was optional prior to POSIX 1003.1-2001).
>
>This adds an autoconf check to decide whether to use pthread_rwlock_t
>or the fallback implementation in terms of std::condition_variable and
>std::mutex.

Actually the autoconf changes aren't needed, as PR 64847 is already
fixed. Maybe it's better to have an explicit check for
pthread_rwlock_t anyway though ... I'll have a think.