Change GC_markers and GC_nprocs type to int

Change GC_markers and GC_nprocs type to int

* include/private/gc_priv.h (GC_markers): Change type from long to int.
* mark.c (GC_markers): Likewise.
* pthread_support.c (GC_nprocs): Likewise.
* pthread_support.c (start_mark_threads, GC_thr_init): Adjust printf
format specifier for GC_markers and GC_nprocs.
* win32_threads.c (GC_thr_init): Likewise.
* pthread_support.c (GC_thr_init): Cast sysconf() result to int.
* win32_threads.c (start_mark_threads, GC_wait_marker,
GC_notify_all_marker): Remove unnecessary cast of GC_markers.
* win32_threads.c (GC_thr_init): Cast dwNumberOfProcessors to int.