Memory consumption optimization while loading ELF debug info:

Memory consumption optimization while loading ELF debug info:
- don't map twice an ELF file for symbol lookup (in non deferred mode)
- no longer entirely map an ELF file into memory, but only the
  sections we need.
Added support for loading ELF modules thru SymLoadModule in a non life
process.
Factorisation of code for ELF module handling.
Fixes to ELF symbol loading
- drops symbols from symtab which are neither funcs nor global
  variables
- fixes some incorrect size computation for latest GCC versions.
Several cleanups and fixes.