Use std::vector in compile-loc2c.c

Use std::vector in compile-loc2c.c

This changes compile-loc2c.c to use std::vector, removing some
cleanups.

gdb/ChangeLog
2017-11-04  Tom Tromey  <tom@tromey.com>

	* compile/compile-loc2c.c (compute_stack_depth_worker): Change
	type of "info".
	(compute_stack_depth): Likewise.
	(do_compile_dwarf_expr_to_c): Use std::vector.