Cygwin: open_shared: don't reuse shared_locations parameter as output

Cygwin: open_shared: don't reuse shared_locations parameter as output

For ages, open_shared uses the shared_locations parameter as
output to indicate if the mapping for a shared region has been
created or just opened.  Split this into two parameters.  Use
the shared_locations parameter as input only, return the creation
state of the mapping in a bool reference parameter.

Conflict: Simple collision due to missing backport of
	  3721a756b0d8 ("Cygwin: console: Make the console accessible from other terminals.")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>