Fix incorrect dwarf block size

Also added assert for zero-length blocks
Link .debug_info to .debug_abbrev via abbrev-offset

This fixes debug info in multiple files - previously all .debug_info
sections were being parsed using the first file's .debug_abbrev section.
Removed unused out_label_dbg_type()
Move .codes into stmt's bits union

Also add begin and end labels for debug output
Label lexical block scopes in debug output
Removed unused decl_sort_cmp()
Function variable offset handled for local variable locations
Dwarf static variable addressing
Output DW_TAG_unspecified_parameters for variadic functions
Debug test files