When several debug formats (eg stabs & dwarf2) exist in the same
module, allow to load them all (this is needed when different
compilation units are compiled with different debug options).

Walking the whole lot, not doing anything interesting apart from
traversing the data.

- split the data structures for walking through the data (abbrev,
  cu... -> traverse_ctx) and data manipulation/loading (-> parse_ctx)
- created dwarf2_parse_compilation_unit() for clarity
- added section structure to gather information about all ELF sections
  related to all dwarf2 sections (more to come)

- correctly set size & offsets for regular udt members
- first shot at bitfields for udt members

- properly handling function blocks
- handling of variables inside of blocks (either on stack, or in a
  register, or relative to the frame register if any)
- added dwarf2_subprogram_t structure so that we can pass around
  relevant information for function parsing

- added the ability to tell to add_func_local whether we're adding
  a local variable or a parameter (and removed the black magic
  we were using)
- we can now address variables defined as an offset to a register

Offset the addresses for global symbols (func & variables) by the base
image of the corresponding module.

- various fixes to follow better the functions definition (nesting,
  subroutines...)
- don't directly parse types referenced by a subprogram, they'll be
  loaded anyway when needed

- put back the block attribute parsing
- added dwarf2_compute_location to properly decode a location (at
  least starting it)

- rewrote all entities loading to make use of new dwarf2_debug_info_t scheme
- commented out the location parsing which is an ugly hack

- add some helpers for the rewrite
- module is now part of the dwarf2_parse_context

Removed unused type references scheme that we'll implement using a
different scheme in next patches.

Merge into a single function the struct/class/union parsing.

- now loading the debug info entries into specific structures
- this will help writing new functions
- this will allow handling of forward references

- added a pool for memory allocation when parsing a compilation unit
- now using the brand new sparse array for the abbrev table

- removed lookup for name for the const modifier
- hard wire dwarf-reference to our pointer types

- we should set the module's symtype upon success
- removed unneeded bRet variable

- AT_byte_size can be larger than a single byte (especially for enums)
- added missing enumeration type parsing

Added types_get_real_type() to get rid of typedef information, and
access the real underlying type.

- NVidia allows "const vec4 = {1.0, 2.0, 3.0, 4.0};", even though
  that's not part of the spec.
- It should be  "const vec4 = vecr4(1.0, 2.0, 3.0, 4.0);"
- This patch fixes this for D3DSIO_DEF and D3DSIO_DEFI.