* elf.c, elfcode.h, libelf.h: Serious reorganization.

* elf.c, elfcode.h, libelf.h: Serious reorganization.
Deleted `thunk' structure, merged into tdata, duplicate data eliminated.
Rearranged functions, grouping by function.
Broke up many functions in elfcode.h, re-ordered many parts of file writing
to handle unpredictable state of section relocation table as provided by
various applications.
Still needs cleanup: Merge functions back together, split out data structure
with only data that is used only when writing out object file.

* elf.c (bfd_elf_generic_reloc): New function, taken from coff-mips.c.
* elf32-sparc.c (elf_sparc_howto_table): Use it, to work around
bfd_perform_relocation lossage.