Bug#42524: Function pthread_setschedprio() is defined but seems broken on i5/OS PASE

The problem is that MySQL use of pthread_setschedprio is not
supported by i5/OS and the default system behavior for unsupported
calls is to emit a SIGILL signal which causes the server to
abort.

The solution is to treat the pthread_setschedprio as inexistent
when compiling binaries for i5/OS. This also does not invalidate
the fix for bug 38477 as the only supported dispatch class is
SCHED_OTHER (which is passed to pthread_setschedparam).

configure.in:
  Skip pthread_setschedprio check on i5/OS.

configure.in

@@ -2048,7 +2048,7 @@ AC_CHECK_FUNCS(alarm bcmp bfill bmove bsearch bzero \
   mkstemp mlockall perror poll pread pthread_attr_create mmap mmap64 getpagesize \
   pthread_attr_getstacksize pthread_attr_setprio pthread_attr_setschedparam \
   pthread_attr_setstacksize pthread_condattr_create pthread_getsequence_np \
-  pthread_key_delete pthread_rwlock_rdlock pthread_setprio pthread_setschedprio \
+  pthread_key_delete pthread_rwlock_rdlock pthread_setprio \
   pthread_setprio_np pthread_setschedparam pthread_sigmask readlink \
   realpath rename rint rwlock_init setupterm \
   shmget shmat shmdt shmctl sigaction sigemptyset sigaddset \
@@ -2071,6 +2071,15 @@ case "$target" in
     ;;
 esac
 
+case "$mysql_cv_sys_os" in
+ OS400) # i5/OS (OS/400) emits a SIGILL (Function not implemented) when
+        # unsupported priority values are passed to pthread_setschedprio.
+        # Since the only supported value is 1, treat it as inexistent.
+    ;;
+ *) AC_CHECK_FUNCS(pthread_setschedprio)
+    ;;
+esac
+
 # Check that isinf() is available in math.h and can be used in both C and C++ 
 # code
 AC_MSG_CHECKING(for isinf in <math.h>)