Cygwin: pthread: Take note of schedparam in pthread_create

Take note of schedparam in any pthread_attr_t passed to pthread_create.

postcreate() (racily, after the thread is actually created), sets the
scheduling priority if it's inherited, but precreate() doesn't store any
scheduling priority explicitly set via a non-default attr to
pthread_create, so schedparam.sched_priority has the default value of 0.

(I think this is another long-standing bug exposed by 4b51e4c1.  Now we
don't lie about the actual thread priority, it's apparent it's not
really being set in this case.)

Fixes testcase priority2.

Signed-off-by: Jon Turney <jon.turney@dronecode.org.uk>

winsup/cygwin/thread.cc

@@ -457,6 +457,7 @@ pthread::precreate (pthread_attr *newattr)
       attr.joinable = newattr->joinable;
       attr.contentionscope = newattr->contentionscope;
       attr.inheritsched = newattr->inheritsched;
+      attr.schedparam = newattr->schedparam;
       attr.stackaddr = newattr->stackaddr;
       attr.stacksize = newattr->stacksize;
       attr.guardsize = newattr->guardsize;