gdb: add inferior parameter to inferior_created observable

gdb: add inferior parameter to inferior_created observable

I think it would make sense for the inferior_created observable to say
which inferior is being dealt with, rather than relying on it being the
current inferior.

This patch adds an inferior parameter to inferior_created, but does not
change the callbacks to use it.

gdb/ChangeLog:

	* aix-thread.c (aix_thread_inferior_created): Add inferior
	parameter.
	* bsd-uthread.c (bsd_uthread_inferior_created): Likewise.
	* dummy-frame.c (cleanup_dummy_frames): Likewise.
	* jit.c (jit_inferior_created): Likewise.
	* linux-thread-db.c (thread_db_inferior_created): Likewise.
	* m68k-linux-tdep.c (m68k_linux_inferior_created): Likewise.
	* observable.h (inferior_created): Likewise.
	* ravenscar-thread.c (ravenscar_inferior_created): Likewise.
	* symfile-mem.c (add_vsyscall_page): Likewise.
	* infcmd.c (post_create_inferior): Pass inferior argument.

Change-Id: I2543d19ff055a9df6b269929faea10b27d2adc5e