Refactoring of android_thread_kill/pthread_kill calls

Refactoring of android_thread_kill/pthread_kill calls

* pthread_stop_world.c (android_thread_kill) [USE_TKILL_ON_ANDROID]:
Move definition upper (to be before its first use); remove forward
declaration.
* pthread_stop_world.c (THREAD_SYSTEM_ID, RAISE_SIGNAL): New macro.
* pthread_stop_world.c (GC_suspend_thread): Remove "result" local
variable
* pthread_stop_world.c (GC_suspend_thread, GC_suspend_all,
GC_start_world): Use RAISE_SIGNAL() instead of pthread_kill and
android_thread_kill.
* pthread_stop_world.c (GC_suspend_all, GC_start_world): Remove
"thread_id" local variable; use THREAD_SYSTEM_ID instead of thread_id.