threads: Removed unneeded Linux Threads check

Remove the "threads have different pids" check, which was really
a check for the old LinuxThreads behavior, as it is no longer
used.  In addition to NPTL being released 17 years ago and the
default basically everywhere, nothing in Open MPI uses the
macro set and this is just dead code at this point.

Signed-off-by: Brian Barrett <bbarrett@amazon.com>

Author: bwbarrett

opal/mca/threads/pthreads/configure.m4

@@ -30,101 +30,6 @@
 # ********************************************************************
 
 
-AC_DEFUN([OPAL_CHECK_PTHREAD_PIDS],[
-#
-# Arguments: none
-#
-# Dependencies: None
-#
-# Sets:
-#  OPAL_THREADS_HAVE_DIFFERENT_PIDS (variable)
-#
-# Test for Linux-like threads in the system.  OPAL no longer supports
-# systems with different PIDs for threads in the same process, so error
-# out if we detect that case.
-#
-
-AC_MSG_CHECKING([if threads have different pids (pthreads on linux)])
-
-OPAL_VAR_SCOPE_PUSH([CFLAGS_save CPPFLAGS_save LDFLAGS_save LIBS_save MSG])
-CFLAGS_save="$CFLAGS"
-CFLAGS="$CFLAGS $THREAD_CFLAGS"
-CPPFLAGS_save="$CPPFLAGS"
-CPPFLAGS="$CPPFLAGS $THREAD_CPPFLAGS"
-LDFLAGS_save="$LDFLAGS"
-LDFLAGS="$THREAD_LDFLAGS"
-LIBS_save="$LIBS"
-LIBS="$THREAD_LIBS"
-AC_RUN_IFELSE([AC_LANG_SOURCE([#include <pthread.h>
-#include <sys/types.h>
-#include <unistd.h>
-#include <stdlib.h>
-
-void *checkpid(void *arg);
-int main() {
-  pthread_t thr;
-  int pid, *retval;
-  pid = getpid();
-  pthread_create(&thr, NULL, checkpid, &pid);
-  pthread_join(thr, (void **) &retval);
-  exit(*retval);
-}
-
-static int ret;
-void *checkpid(void *arg) {
-   int ppid = *((int *) arg);
-   if (ppid == getpid())
-     ret = 0;
-   else
-     ret = 1;
-   pthread_exit((void *) &ret);
-}])],
-[MSG=no OPAL_THREADS_HAVE_DIFFERENT_PIDS=0],
-[MSG=yes OPAL_THREADS_HAVE_DIFFERENT_PIDS=1],
-[
- # If we're cross compiling, we can't do another AC_* function here because
- # it we haven't displayed the result from the last one yet.  So defer
- # another test until below.
- OPAL_THREADS_HAVE_DIFFERENT_PIDS=
- MSG="cross compiling (need another test)"])
-
-CFLAGS="$CFLAGS_save"
-CPPFLAGS="$CPPFLAGS_save"
-LDFLAGS="$LDFLAGS_save"
-LIBS="$LIBS_save"
-
-AC_MSG_RESULT([$MSG])
-
-AS_IF([test "x$OPAL_THREADS_HAVE_DIFFERENT_PIDS" = "x"],
-      [ # If we are cross-compiling, look for the symbol
-       # __linuxthreads_create_event, which seems to only exist in the
-       # Linux Threads-based pthreads implementation (i.e., the one
-       # that has different PIDs for each thread).  We *could* switch
-       # on $host here and only test *linux* hosts, but this test is
-       # pretty unique, so why bother?  Note that AC_CHECK_FUNC works
-       # properly in cross-compiling environments in recent-enough
-       # versions of Autoconf (which is one of the reasons we mandate
-       # recent versions in autogen!).
-       AC_CHECK_FUNC([__linuxthreads_create_event],
-                     [OPAL_THREADS_HAVE_DIFFERENT_PIDS=1])])
-
-AS_IF([test "$OPAL_THREADS_HAVE_DIFFERENT_PIDS" = "1"],
-      [AC_MSG_WARN([This version of Open MPI only supports environments where])
-       AC_MSG_WARN([threads have the same PID.  Please use an older version of])
-       AC_MSG_WARN([Open MPI if you need support on systems with different])
-       AC_MSG_WARN([PIDs for threads in the same process.  Open MPI 1.4.x])
-       AC_MSG_WARN([supports such systems, as does at least some versions the])
-       AC_MSG_WARN([Open MPI 1.5.x series.])
-       AC_MSG_ERROR([Cannot continue])
-      ])
-
-#
-# if pthreads is not available, then the system does not have an insane threads
-# model
-#
-OPAL_VAR_SCOPE_POP
-])dnl
-
 AC_DEFUN([OPAL_INTL_PTHREAD_TRY_LINK], [
 # BEGIN: OPAL_INTL_PTHREAD_TRY_LINK
 #
@@ -774,8 +679,6 @@ THREAD_CXXCPPFLAGS="$TPKG_CXXCPPFLAGS"
 THREAD_LDFLAGS="$TPKG_LDFLAGS"
 THREAD_LIBS="$TPKG_LIBS"
 
-OPAL_CHECK_PTHREAD_PIDS
-
 AS_IF([test "$CXX" = "no"], [opal_pthread_cxx_success=1])
 
 if test "$OMPI_TRY_FORTRAN_BINDINGS" = "$OMPI_FORTRAN_NO_BINDINGS" || \