Use std::vector for moribund_locations

Use std::vector for moribund_locations

This changes moribund_locations to use a std::vector rather than VEC.
I also noticed that moribund_locations is only used in breakpoint.c,
so now it is static as well.

It might be possible to make this code a bit simpler by using a
ref_ptr in moribund_locations; however, I have not done this.

Tested by the buildbot.

gdb/ChangeLog
2018-07-10  Tom Tromey  <tom@tromey.com>

	* breakpoint.c (moribund_locations): Now static and a
	std::vector.
	(breakpoint_init_inferior, moribund_breakpoint_here_p)
	(build_bpstat_chain, update_global_location_list)
	(breakpoint_retire_moribund): Update.
	* breakpoint.h (bp_location_p): Remove typedef.  Don't declare
	VEC.