Pthreads detection (ITS#587)

[sascha@schumann.cx]

    Hi,

    I'm involved with the Apache 2.0 and PHP projects which both
    need to detect Pthreads in a portable way. I noticed that the
    OpenLDAP project also uses threads and that it has its own
    way of detecting the platform-dependent options.

    Our effort aims at sharing our knowledge about how Pthreads
    can be found and activated on various platforms. That is why
    we have encapsulated the Pthreads detection autoconf code. We
    currently support these systems:

     -kthread          gcc (FreeBSD)
     -Kthread          UDK cc (UnixWare)
     -mt               WorkShop cc (Solaris)
     -mthreads         gcc (AIX)
     -pthread          gcc (Linux, FreeBSD, NetBSD, OpenBSD)
     -pthreads         gcc (Solaris)
     -qthreaded        AIX cc V5
     -threads          gcc (HP-UX)                                              

    The autoconf code is easy to integrate into other build
    systems. Let me know, if you are interested in this stuff.
    
    - Sascha