PTHREAD_ONCE_INIT on Solaris

[Kevin Ryde]

I'm thinking of something like this for PTHREAD_ONCE_INIT on Solaris
reported by Claes Wallin on bug-guile.

        #if SCM_NEED_BRACES_ON_PTHREAD_ONCE_INIT
        #define SCM_I_PTHREAD_ONCE_INIT             { PTHREAD_ONCE_INIT }
        #else
        #define SCM_I_PTHREAD_ONCE_INIT             PTHREAD_ONCE_INIT
        #endif

SCM_NEED_BRACES_ON_PTHREAD_ONCE_INIT would be in scmconfig.h.  I guess
SCM_I_PTHREAD_ONCE_INIT is internal-only at the moment so maybe the
configury only needs to go in config.h, but pthread-threads.h is an
installed header, so I'm thinking scmconfig.h and an "SCM_" name is
best.