Use new and delete for struct infcall_control_state

Use new and delete for struct infcall_control_state

This changes infrun.c to use new and delete for infcall_control_state.

gdb/ChangeLog
2018-09-17  Tom Tromey  <tom@tromey.com>

	* gdbthread.h (struct thread_control_state): Add initializer.
	(class thread_info) <control>: Remove initializer.
	* inferior.h (struct inferior_control_state): Add initializer.
	(class inferior) <control>: Remove initializer.
	(exit_inferior_1): Update.
	* infrun.c (struct infcall_control_state): Add constructors.
	(save_infcall_control_state): Use new.
	(restore_infcall_control_state, discard_infcall_control_state):
	Use delete.