Cygwin: pinfo: raise MAX_PID to 4194304

Reportedly, the maximum pid of 65536 is much too small in bigger
environments.  Raise the maximum PID to 4194304, whihc is the maximum
pid on Linux (PID_MAX_LIMIT defined in include/linux/threads.h).

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/local_includes/pinfo.h

@@ -223,7 +223,7 @@ private:
   DWORD status_exit (DWORD);
 };
 
-#define MAX_PID 65536
+#define MAX_PID 4194304
 
 #define ISSTATE(p, f)	(!!((p)->process_state & f))
 #define NOTSTATE(p, f)	(!((p)->process_state & f))

winsup/cygwin/pinfo.cc

@@ -239,7 +239,7 @@ pinfo::exit (DWORD n)
 }
 # undef self
 
-/* Return next free Cygwin PID between 2 and 65535, round-robin.  Each new
+/* Return next free Cygwin PID between 2 and MAX_PID, round-robin.  Each new
    PID is checked that it doesn't collide with an existing PID.  For that,
    just check if the "cygpid.PID" section exists. */
 pid_t

winsup/cygwin/release/3.6.0

@@ -74,3 +74,7 @@ What changed:
   '(18) priority' is now set to the negated sched_policy minus one.
   If SCHED_IDLE is selected, this field is set to 39.  The '(19) nice'
   field is now set to the originally requested nice value.
+
+- Raise maximum pid from 65536 to 4194304 to account for scenarios
+  with lots of CPUs and lots of tasks.
+  Addresses: https://cygwin.com/pipermail/cygwin/2024-December/256927.html