gdb/

	Support constant DW_AT_data_member_location by GCC PR debug/40659.
	* dwarf2read.c
	(dwarf2_add_field <DW_TAG_member> <DW_AT_data_member_location>):
	Initialize BYTE_OFFSET to 0 by default.  Explicitly check if
	attr_form_is_block.
	(dwarf2_add_field <DW_TAG_inheritance> <DW_AT_data_member_location>)
	(read_common_block <DW_AT_data_member_location>): New variable
	byte_offset.  Fix crash on non-DW_BLOCK ATTR values.

gdb/testsuite/
	Support constant DW_AT_data_member_location by GCC PR debug/40659.
	* gdb.dwarf2/dw2-inheritance.exp, gdb.dwarf2/dw2-inheritance.S: New.