z/OS: Updated portability notes

Updated:
    builds/zos/README.md: Updated with portability notes resulting
       from building zeromq/libzmq/master as of 2014-07-23 on z/OS
       UNIX System Services.

       Current z/OS UNIX status: all expected tests pass, except
       "test_proxy", which hangs and times out.

builds/zos/README.md

@@ -12,6 +12,8 @@ Tested build combinations:
 
 * ZeroMQ 4.0.4, using IBM XL C/C++ compiler, as XPLINK in LP64 mode
 
+* ZeroMQ 4.1-git, using IBM XL C/C++ compiler, as XPLINK in ILP32 mode
+
 Other combinations are likely to work, possibly with minor changes,
 but have not been tested.  Both static library and DLL modes have been
 tested.
@@ -201,9 +203,18 @@ pass. There are two tests that are expected to fail:
     programs -- most programs use threads or fork without exec, but
     not both.
 
-These two "expected to fail" tests are listed as XFAIL_TESTS, and
+0.  `test_diffserv`: tests ability to set IP_TOS ([IP Type of
+    Service](http://en.wikipedia.org/wiki/Type_of_service), or
+    [DiffServ](http://en.wikipedia.org/wiki/Differentiated_Services_Code_Point))
+    values on sockets.  While z/OS UNIX System Services has the
+    preprocessor defines required, it appears not to support the
+    required functionality (call fails with "EDC8109I Protocol not
+    available.")
+
+These three "expected to fail" tests are listed as XFAIL_TESTS, and
 `runtests` will still consider the test run successful when they fail
-as expected.
+as expected.  (`builds/zos/runtests` will automatically skip these
+"expected to fail" tests if running "all" tests.)
 
 In addition `test_security_curve` does not do any meaningful testing,
 as a result of the CURVE support not being compiled in; it requires
@@ -212,6 +223,13 @@ ported to z/OS UNIX System Services yet.
 
 Multicast (via `libpgm`) is also not ported or compiled in.
 
+[TIPC](http://hintjens.com/blog:70), a cluster IPC protocol,
+is only supported on Linux, so it is not compiled into the z/OS
+UNIX System Services port -- and the tests are automatically skipped
+if running "all" tests.  (However they are not listed in XFAIL_TESTS
+because without the TIPC support there is no point in even running
+them, and it would be non-trivial to track them by hand.)
+
 
 ## ZeroMQ on z/OS UNIX System Services: Library portability notes
 
@@ -278,6 +296,18 @@ which is done in the `cxxall` script.  (The "3" value exposes later
 pthreads functionality like `pthread_atfork`, although ZeroMQ does not
 currently use all these features.)
 
+If compiling on a *recent* version of z/OS UNIX System Services it
+may be worth compiling with:
+
+    _UNIX03_THREADS=1
+
+which enables a later version of the threading support, potentially
+including `pthread_getschedparam` and pthread_setschedparam`; at
+present in the z/OS UNIX System Services port these functions are
+hidden and never called.  (See [IBM z/OS pthread.h
+documentation](http://pic.dhe.ibm.com/infocenter/zos/v1r11/index.jsp?topic=/com.ibm.zos.r11.bpxbd00/pthrdh.htm)
+for details on the differences.)
+
 
 ## `platform.hpp` on z/OS UNIX System Services
 
@@ -286,6 +316,11 @@ pre-built `platform.hpp` file.  (By default `src/platform.hpp` is
 dynamically generated as a result of running the `./configure` script.)
 The master version of this is in `builds/zos/platform.hpp`.
 
+Beware that this file contains the version number for libzmq (usually
+included during the configure phase).  If taking the `platform.hpp` from
+an older version to use on a newer libzmq be sure to update the version
+information near the top of the file.
+
 The pre-built file is used because z/OS does not have the GNU auto tools
 (`automake`, `autoconf`, `libtool`, etc) installed, and particularly the
 libtool replacement does not work properly with the IBM XL C/C++
@@ -317,18 +352,20 @@ syntax):
 
 *   set `CPPFLAGS` to for the feature macros required, eg:
 
-        setenv CPPFLAGS "-D_XOPEN_SOURCE_EXTENDED=1 -D_OPEN_THREADS=3 -D_OPEN_SYS_SOCK_IPV6"
+        setenv CPPFLAGS "-D_XOPEN_SOURCE_EXTENDED=1 -D_OPEN_THREADS=3 -D_OPEN_SYS_SOCK_IPV6 -DZMQ_HAVE_ZOS"
 
 *   set `CXXFLAGS` to enable XPLINK:
 
         setenv CXXFLAGS "-Wc,xplink -Wl,xplink -+"
 
 *   run configure script with `--disable-eventfd` (`sys/eventfd.h` does
-    not exist, but the test for its existance has a false positive on 
+    not exist, but the test for its existance has a false positive on
-    z/OS UNIX System Services, apparently due to the way the `c++` 
+    z/OS UNIX System Services, apparently due to the way the `c++`
-    compiler wrapper passes errors back from the IBM XL C/C++ compiler), viz:
+    compiler wrapper passes errors back from the IBM XL C/C++ compiler),
+    and with `--with-poller=poll` because `poll` is the most advanced
+    of the file descriptor status tests available on z/OS.  That is:
 
-        ./configure --disable-eventfd
+        ./configure --disable-eventfd --with-poller=poll
 
 All going well several Makefiles, and `src/platform.hpp` should be
 produced.  Two additional changes are required to `src/platform.hpp`