Throughout, change check for running under Windows NT to 'iswinnt'.

* dcrt0.cc (set_os_type): Set 'iswinnt' appropriately.
* cygheap.cc (init_cheap): Revert to using VirtualAlloc for allocating cygheap.
(cygheap_setup_for_child_cleanup): New function.  Standard function to call
after calling CreateProcess to cleanup cygheap info passed to child.
(cygheap_fixup_in_child): Copy cygheap from shared memory into allocated space
under Windows 9x or if can't relocate shared space under NT.
* cygheap.h: Declare new function.
* spawn.cc (spawn_guts): Use cygheap_fixup_in_child.
* fork.cc (fork_parent): Ditto.
* winsup.h: Declare iswinnt.

winsup/cygwin/pinfo.h

@@ -185,7 +185,7 @@ public:
 extern __inline pid_t
 cygwin_pid (pid_t pid)
 {
-  return (pid_t) (os_being_run == winNT) ? pid : -(int) pid;
+  return (pid_t) (iswinnt) ? pid : -(int) pid;
 }
 
 void __stdcall pinfo_init (char **, int);