Fix more typos in comments

* darwin_stop_world.c (GC_use_threads_discovery): Fix a typo in
comment ("stopped").
* doc/porting.html: Fix typos in comment ("defining", "support").
* include/gc.h (GC_get_prof_stats): Fix a typo in comment ("entries").
* include/private/gc_priv.h (GC_have_errors): Fix a typo in comment
("OK").
* include/private/gcconfig.h: Fix a typo in comment ("SPARC).
* ChangeLog: Likewise.
* os_dep.c (GC_linux_main_stack_base): Likewise.
* include/private/gcconfig.h: Fix a typo in comment ("release").
* mallocx.c (GC_generic_malloc_many): Fix a typo in comment
("reacquiring").
* mallocx.c (GC_memalign): Fix a typo in comment ("OK").
* os_dep.c (GC_win32_free_heap): Likewise.
* pthread_support.c (GC_remove_all_threads_but_me): Likewise.
* win32_threads.c (GC_remove_all_threads_but_me): Likewise.
* doc/README.Mac: Likewise.
* mark.c (GC_push_unconditionally): Fix a typo in comment ("pointers").
* pthread_support.c: Fix a typo in comment ("which").
* win32_threads.c: Fix a typo in comment ("losing").