Use std::vector in struct catch_syscall_inferior_data

Use std::vector in struct catch_syscall_inferior_data

This changes struct catch_syscall_inferior_data to use a std::vector
rather than a VEC.  It also changes it to be allocated with new and
destroyed with delete.

ChangeLog
2017-07-22  Tom Tromey  <tom@tromey.com>

	* break-catch-syscall.c (struct catch_syscall_inferior_data)
	<syscalls_counts>: Now a std::vector.
	(get_catch_syscall_inferior_data): Use "new".
	(catch_syscall_inferior_data_cleanup): Use "delete".
	(insert_catch_syscall, remove_catch_syscall)
	(clear_syscall_counts): Update.