Some cleanup removal in dwarf2loc.c

Some cleanup removal in dwarf2loc.c

This removes some cleanups and manual allocation handling in
dwarf2loc.c with std::vector.  Note that this patch has a case where
the vector would normally fall into the "use gdb::unique_ptr"
guidelines -- but here because the vector is immediately initialized,
I moved the initialization into the constructor call, for further
code savings.

2016-10-21  Tom Tromey  <tom@tromey.com>

	* dwarf2loc.c: Include <vector>.
	(read_pieced_value, write_pieced_value)
	(dwarf2_compile_expr_to_ax): Use std::vector.