Write LF_POINTER CodeView types for pointers to member functions or data

Write LF_POINTER CodeView types for pointers to member functions or data

Translate DW_TAG_ptr_to_member_type DIEs into special extended
LF_POINTER CodeView types.

gcc/
	* dwarf2codeview.cc (struct codeview_custom_type): Add new fields to
	lf_pointer struct in union.
	(write_lf_pointer): Write containing_class and ptr_to_mem_type if
	applicable.
	(get_type_num_subroutine_type): Write correct containing_class_type if
	this is a pointer to a member function.
	(get_type_num_ptr_to_member_type): New function.
	(get_type_num): Call get_type_num_ptr_to_member_type.
	* dwarf2codeview.h (CV_PTR_MODE_MASK, CV_PTR_MODE_PMEM): Define.
	(CV_PTR_MODE_PMFUNC, CV_PMTYPE_D_Single, CV_PMTYPE_F_Single): Likewise.