ELF Tool Chain Code

Renamed DWARF_E_MEMORY to DW_DLE_MEMORY.

Ticket: #20

* Renamed DWARF_E_ARGUMENT to DW_DLE_ARGUMENT.
* Renamed DWARF_E_DEBUG_INFO to DW_DLE_DEBUG_INFO_NULL.

Substitute DWARF_E_NONE with DW_DLE_NONE.

Ticket: #20

Minimal instruction length should depend on ISA: 1 for X86 and
X86_64, 4 for other ISA. (for now, this needs more investigation)

* Add at_relsec field into _Dwarf_Attribute structure. at_relsec represent a relocation refering to dwarf sections. This is needed because attribute values can refer to other dwarf sections. For example, DW_AT_stmt_list refers to an offset in .debug_line section.
* Add internal function _dwarf_add_AT_dataref that can accpet both a relocation symbol index and a relocation section name.
* Insert DW_AT_stmt_list attribute into compilation unit DIE if there are line number information.

Document the purpose of the die arg for producer API dwarf_add_frame_fde[_b].

Do not try to generate empty name lookup table.

Produce .debug_pubnames, .debug_weaknames, .debug_funcnames,
.debug_typenames and .debug_varnames sections.

Name lookup table producer APIs keep a pointer to the refered DIE. The
offset of this DIE will be known after DIE transform. _dwarf_nametbl_gen
is called after DIE transform and it will write the known offset into
bytes stream.

Implemented producer API for name lookup sections: dwarf_add_funcname,
dwarf_add_pubname, dwarf_add_typename, dwarf_add_varname and
dwarf_add_weakname.