gdb/

gdb/
	* dwarf2loc.c (struct dwarf_expr_baton) Replace objfile by per_cu.
	(dwarf_expr_tls_address): Use per_cu instead of objfile.
	(dwarf2_evaluate_loc_desc): Drop initialization of BATON.OBJFILE.
	Initialize new BATON.PER_CU.  Adjust CTX->GDBARCH initialization for
	this change.
	(struct needs_frame_baton): New field per_cu.
	(dwarf2_loc_desc_needs_frame): Initialize new BATON.PER_CU.
	* dwarf2read.c (struct dwarf2_per_cu_data) <cu>: Extend the comment.